Going to spray flea spray in my backyard, how long do I have to wait to let my dogs go in the back?

I am going to spray this stuff 'enforcer' flea spray in my backyard because every time I let my dogs out back, they come in and I pick fleas (or ticks, not sure which is which.) off them. And they take the medicine from their dr. the help prevent fleas and ticks. But how long would you suggest I wait to let them go back in the back? I read and reread the instructions to see, but it doesn't say. SOMEONE HELP PLEASE! Thanks!