In my experiences, there is no "set time", and it just depends on the birds whether they will come back to the same roost that evening after being scared off that morning. I guess it depends on what (how) they were scared off the roost. If you know of a pretty reliable area where the birds go to roost, get there about an hour and 1/2 to 2 hrs before dark and set up doing some light calling (purrs, clucks) and try to convince a tom to roost where you are. Remember, it is easier to get a tom to come to you when your close to where he wants to be anyway.