Why does the voting continue far beyond this time limit?
Emboldened is quoted text, below.
House Voting Procedures: Forms and Requirements, Updated February 6, 2019, p 3.
Length of Time for Voting
Under Rule XX, clause 2(a), the minimum time for a vote by electronic device is 15 minutes in either the House or the Committee of the Whole. The 15-minute period is the minimum time allowed, rather than the maximum, for the conduct of a recorded vote. The chair has the discretion to hold the vote open longer.
The voting period for some votes may be shorter than 15 minutes under certain circumstances. The Speaker may reduce the voting time to not less than five minutes (Rule XX, clause 9) “on any question that follows another electronic vote or a report from the Committee of the Whole, if in the discretion of the Speaker Members would be afforded an adequate opportunity to vote.” Certain votes in the Committee of the Whole may also be reduced to not less than two minutes, as noted in Rule XVIII, clause 6.