OPINION

Terry Peppers appeals, pro se, from a District Court order denying his request to reopen the District Court’s prior decision denying his request for a modification of sentence. For the reasons that follow, we will summarily affirm the District Court’s order.

I. Background

Peppers pleaded guilty to firearm offenses in violation of 18 U.S.C. § 922(g)(1), and he was sentenced in May 2007 to a term of 130 months of imprisonment. In March 2008, Peppers sent a letter to the District Court “regarding an] article [he] read in [T]he Star Ledger about Passaic County Jail,” and asked “[if he was] eligible for any ... downward [sentencing] departure?” The District Court construed the letter as a request to modify his sentence pursuant to Rule 35 of the Federal Rules of Criminal Procedure, and in July 2008 the District Court denied the request as untimely. 1 Peppers did not appeal. In *703 June 2011, he filed a motion, citing Rule 60(b) of the Federal Rules of Civil Procedure, arguing that he had intended his letter to be a timely motion under 28 U.S.C. § 2255. The District Court denied the motion by order entered December 13, 2011, and Peppers appeals.

II. Jurisdiction

We begin with a question of appellate jurisdiction. The District Court construed Peppers’ March 2008 letter as a motion under the Federal Rules of Criminal Procedure. That construction was entirely plausible, and Peppers did not timely appeal it. Peppers much later filed a motion for reopening, citing the Federal Rules of Civil Procedure. Although the Federal Rules of Civil Procedure are not applicable to criminal cases, motions for reopening and reconsideration may, of course, be filed in criminal cases. See United States v. Fiorelli, 337 F.3d 282, 286 (3d Cir. 2003). Under these circumstances, we think it proper to apply the rules governing appeals in criminal cases. Thus, Peppers had 14 days to appeal the District Court’s denial of reopening. See Fed. R.App. P. 4(b)(1)(A).

The District Court did not receive Peppers’ notice of appeal until January 4, 2012, 22 days after the entry of the District Court’s order. Peppers, however, is entitled to the benefit of the prison mailbox rule, see Houston v. Lack, 487 U.S. 266, 270-72, 108 S.Ct. 2379, 101 L.Ed.2d 245 (1988), and he turned his notice of appeal over to prison officials on December 30, 2011, only three days beyond the Fed. RApp. P. 4(b) deadline. Peppers has also alleged that it took eight days for the District Court’s order to reach him. In an appropriate case, we might ask the District Court for factfinding as to how much of the time delay was attributable to the prison. See United States v. Grana, 864 F.2d 312, 313 (3d Cir. 1989); see also Long v. Atlantic City Police Dep’t, 670 F.3d 436, 443-44 (3d Cir. 2012) (reaffirming Grana’s ■vitality). We need not do so here, though, because the 14-day period for appeals in a criminal case is non-jurisdictional, see Virgin Islands v. Martinez, 620 F.3d 321, 329 (3d Cir. 2010), and the Government has not pressed the timeliness issue. 2 We therefore turn to the merits. We review the District Court’s denial of a motion for reconsideration for an abuse of discretion only. See Max’s Seafood Cafe ex rel. Lou-Ann, Inc. v. Quinteros, 176 F.3d 669, 673 (3d Cir. 1999).

III. Discussion

Under the version of Rule 35(a) applicable to Peppers, 3 “[wjithin 7 days after sentencing, the court may correct a sentence that resulted from arithmetical, technical, or other clear error.” This seven-day time limit is jurisdictional. United States v. Higgs, 504 F.3d 456, 463 (3d Cir. 2007) (contrasting the time limit in Rule 35 with the Supreme Court’s decision in Eberhart v. United States, 546 U.S. 12, 126 S.Ct. 403, 163 L.Ed.2d 14 (2005), regarding Rule 33). In this case, Peppers was sentenced in May 2007 and he filed his letter, which was construed as a Rule 35 motion, in March 2008. The District Court, there *704 fore, understandably determined that it lacked jurisdiction to modify Peppers’ sentence under Rule 35. Nothing in Peppers’ motion to reopen called the District Court’s jurisdictional analysis or timeliness calculation into question in any way. 4

Peppers now argues that the District Court was required to allow him an opportunity to challenge the characterization of his letter as a Rule 35 motion. In support, he cites Castro v. United States, 540 U.S. 375, 124 S.Ct. 786, 157 L.Ed.2d 778 (2003), and United States v. Miller, 197 F.3d 644 (3d Cir. 1999). Peppers misapprehends those opinions. In Castro and Miller, the courts were concerned about the strict limitations that the Antiterrorism Effective Death Penalty Act (“AEDPA”) placed on § 2255 motions. Castro, 540 U.S. at 377, 124 S.Ct. 786; Miller, 197 F.3d at 645. Therefore, in Castro, the Supreme Court held that “when a court recharacterizes a pro se litigant’s [pleading] as a first § 2255 motion[,] ... the district court must notify the pro se litigant that it intends to rechar-acterize the pleading, warn the litigant ... [of] the restrictions on ‘second or subsequent’ motions, and provide the litigant an opportunity to withdraw the motion or to amend it so that it contains all the § 2255 claims he believes he has.” 540 U.S. at 383, 124 S.Ct. 786. Miller was similarly concerned about ensuring that a movant be allowed to make a knowledgeable decision before proceeding via § 2255. The opinions do not require district courts, as here, to make a searching inquiry before treating a letter a something other than a § 2255 motion. See 197 F.3d at 646.

Here, there was no indication that Peppers’ March 2008 letter challenged his conviction or incarceration in a way § 2255 anticipates, 5 as Peppers’ letter simply stated that “[he was] curious to know [if his sentence was] eligible for any ... downward departure.” While a court must construe a pro se litigant’s pleadings liberally, see Haines v. Kerner, 404 U.S. 519, 520, 92 S.Ct. 594, 30 L.Ed.2d 652 (1972), it need not act as his advocate, see Pliler v. Ford, 542 U.S. 225, 231, 124 S.Ct. 2441, 159 L.Ed.2d 338 (2004). The District Court generously treated Peppers’ brief letter as a Rule 35 motion. Peppers has not now shown that the District Court erred somehow by failing to do more.

Accordingly, we will summarily affirm the District Court’s order. 6