what clock times equal ninety degrees other than 3oclock and 9oclock?

Answer 1

Poorly asked question... What starting point is needed??

See, 1o'clock is 90* from 10 o'clock.... 5o'clock is 90* from 2 o'clock...

So where do you want to start? If you start at 12, only 3 and 9 are 90* away.

Answer 2

With minor approximations, 4:06, 5:12, 6:13, etc.

Going the other way, again with minor approximations, 7:54, 6:48, 5:42, etc.