I have started feeding my slings bigger and bigger crickets up to the point now where the crickets are bigger than the slings.Just to be safe I squash the crickets first.The problem is I do not know how long I should leave the crickets in for before cleaning up.Tonight one of my B boehmei was still sitting right on top of the cricket ,it looked like it was still feeding on it and its been 3 days.When should I throw the crickets out?

All leftovers should be removed by at least the next day as it can start going bad...

Well it should be up to you if your Tarantulas are still feeding on it then leave it, but if the tarantula has thrown it away in the one corner then remove it .(Usaully our Tarantulas store there food in a ball of webbing to eat later so what we think is bad food is what the spider wonts to eat later!)
Or if it goes black then remove it!, or smells bad remove it!
If you add Isopods into your enclosure they will take care of the left over cricket and sort it out for you!
Does not mean you must not keep the cage clean but it will help you!

Cascade you are right ,the crickets are almost completly covered in webbing.