What is the safe time slot to stay in office? Is it 3-5 or 5-7? Anybody getting emails for 3-5?

Nothing is safe. Even people with 9+ hrs are getting terminated.

Yes I got the mail for hours non-compliance

I don't believe you will be safe even doing 9+ hrs, it's just an excuse. If you are already in their list they will find multiple excuses to terminate you regardless of ur WFO hours. Similarly, if you are not on their hitlist, they will not do any arm to you even if you go less than 3 hrs.

Got call from HR for below 5 hrs. Hr mentioned there is no minimum hours and as per policy need to maintain 9 hrs.

With current situation better to maintain 6-7 hrs

told earlier also bottom line matters all this will be an excuse

nothing is clear. Spend as much time as possible.