Unless you are specifically advised on the day of travel that you may remain at the lounge or, more precisely, that you may delay your gate time, you should plan on being at the gate prior to the gate deadline. Playing statistical games is a bad idea. That flight could operate an hour late on each of the last 89 days and on your specific date, operate on schedule.

It also is not worth timing around a 15-20 minute hold on the push while the taxi time is irrelevant to the passenger and is all included -- not added on --- to the scheduled time for the flight.