Short answer. You should ask before the deadline passes, not after. Rule 124, Section 5 allows extension of time to file briefs only for good and sufficient cause, and only if the motion for extension is filed before the expiration of the time sought to be extended — a late motion falls outside what the rule permits.
What the law says
Extension of time for the filing of briefs will not be allowed except for good and sufficient cause and only if the motion for extension is filed before the expiration of the time sought to be extended.
Rule 124, Section 5 — Extension of time for filing briefs. Read the full provision →
Two conditions must both be met
Section 5 does not treat brief-filing extensions as routine. It sets two conjunctive conditions: there must be good and sufficient cause for the extension, and the motion asking for it must be filed before the original period to file the brief actually expires. Both must be satisfied together. Meeting only the good-cause standard while filing after the deadline has already lapsed will not satisfy Section 5's requirements.
Why timing is treated as strictly as the reason itself
A party cannot let the deadline lapse and then argue for an extension after the fact — the rule's structure requires the request to come while time still remains. This puts the burden on counsel to anticipate delay early and file the motion for extension well before the clock runs out, not once it already has. Courts treat the filing-before-expiration requirement as a bright line, not merely a preference, precisely because appeal periods are jurisdictional in nature.
What 'good and sufficient cause' implies
The rule does not define the phrase exhaustively, but by pairing it with a strict filing-before-expiration requirement, it signals that extensions are the exception rather than the norm in appellate brief practice. Counsel seeking more time should be prepared to justify the request on its merits, not merely cite general busyness or convenience. Because the rule does not spell out an exhaustive list, counsel is generally expected to point to a concrete, case-specific circumstance rather than a general scheduling difficulty.
What is at stake in a criminal appeal specifically
Missing the window to move for an extension in a criminal appeal can mean the appellant's brief is never properly filed within an allowable period, jeopardizing the appeal itself. Given how much rides on the brief being accepted, counsel handling a criminal appeal has particular reason to track the filing deadline closely and move early rather than risk running out the clock. Section 5 binds appellant and appellee alike whenever either side needs more time for a brief; it does not distinguish between them, and neither side gets a second chance to ask once its own period to file has already run out without a timely motion on record.