Cramping CAN mean ovulation, but not all craming IS ovulation (IYKWIM). You can also show ALL signs including cramping and still not pop the egg.

The only true indicators of ovulation are a) clear and sustained thermal shift b) bloodwork and c) pregnancy.

A positive OPK is a very good sign, but shouldn't be relied upon totally. As to which day it was, you would normally ovulate 12 - 24 hours after a positive OPK which would possibly make Tuesday 1dpo but cannot be confirmed unless your temp shifted at the same time.

For example, for me, I had two + OPKs (Monday, Tuesday) but didn't see a temp shift until yesterday and confirmed further by another rise today. If my temp goes up again tomorrow I expect to see an O day of Tuesday which will be CD12.

LIsa