Can I ask for extra time on closing day if my lawyer finds a last-minute problem?

Yes, and this is common practice rather than something unusual to request. Parties can agree to extend the closing time or date, and a purchase agreement doesn't automatically terminate simply because the originally scheduled hour or day has passed — as long as both sides, or specifically the party entitled to insist on the original timing, agree to the extension. This is typically documented through a short amending letter between the lawyers rather than anything elaborate.

If the other side won't agree to any extension at all, the situation shifts into a harder question: whether their refusal to allow reasonable time to sort out a genuine last-minute problem is itself unreasonable, or whether you're the one without a solid basis to delay. That assessment depends heavily on what the problem actually is and what the agreement says about timing and conditions. Trust your lawyer's read on whether to press for the extension formally or whether proceeding, waiving the issue, or walking away is the better call in that specific situation.