Timing told by BB are never accurate. It’s always 1:00,1:15,1:30,1:45, 2:00
Like this. They never mention the exact time.
Even going by your logic that they round it off to the nearest quarter hour, the earliest the announcement for Vishal to be entered could have been made at 8:08 PM(because 8:07 PM should be called 8:00PM and not 8:15PM) after that he went to the dome entered it and lied and waited before the signal of time start came. All these must have taken at least one minutes time do he started at 8:09PM
Once his counting was over, he hit the buzzer, tried to come out of the door by himself was unsuccessful, asked Paras for help who ignored him and then Asim came for his support. Once he was out then BB announced for Mahira to enter(time stamp 8:30) this timr after Vishal hitting the buzzer to BB asking for Mahira would have also taken at least one minute considering the amount of things which happened in between.
Now latest time by which announcement for Mahira could have been made was 8:37 PM since 8:38 PM neared out to nearest quarter hour becomes 8:45. So latest time by which Vishal could have hit the buzzer was 8:36 PM
Calculating from both the sides, the maximum time that Vishal could have been counting could be 8:36PM-8:09 PM which is 27 minutes, still on a very high side but much less than 33.xx minutes that BB said.
Doesn't it clearly show that they openly cheat so how can we assume that he did actually count for too long?