How long after sex should I check cm???

Hi

I always check my cm especially this week as it’s my fertile week and I have seen some ewcm every day.

Can you tell me - is there a length of time I should wait after sex to check my cm so it isn’t confused with semen? Should anything after 12 hours not be counted as semen?

I know about the water test but sometimes it’s not practical when your at work so I’d rather avoid checking for a certain length of time after sex. Xxxx