as soon as 'combinedly transactions valued at 20000 settled' you'll get the points. In amex, settlement takes at max. 2 days. So, as soon as you complete in that calendar month 20000 then within 2 days you should see points. If not some transaction still not completed or reversed mostly, check once else wait default wait time till month end.
You don't have to wait till month end everytime but if any issues that is the default response and wait period to get points (you'll get for surely by that month end). Still issues, have to check with support about the reason.