yep, set yourself a limit and respect it. My strategy is not very strict but I always respect the 3-times rule.
1- I give the girl 2 chances
If her two reasons don't seem legit, I will only give two chances. If a girl gives me stupid excuses like "I'm tired" twice or "I have a lot or work to do", I only give two chances. She is obviously not interested to make some space for you in her schedule.
2- I give the girl 3 chances
However, if her two reasons seem legit or at least one is clearly legitimate, I will give it a 3rd try. Sometimes it's hard to judge if the girl is being honest or not. In fact, If she tells me "I really can't tonight, my parents are in Italia and I need to watch for my brother!!

" and on the 2nd try she says "Sorry too much school stuff to do on saturday

". In this case, I'd give a 3rd try because the 1st is very unlikely to be a lie and idk for the 2nd.
After the 3rd try, neeeeeeeeeeexxxxxxxxxttttttt