Not trying to be combative Chuck, seriously. I am only going with my direct dealings with our attorneys, State Officials and many, many hours of 'informative' meetings with all of them for over a period of many months.
Yes, you can state that the work is specific and that it cannot start until after a certain time such as when the client's' staff have left the building. This is something that is required to do the job properly without interference from others. But according to all the personal experiences that I went through; you cannot direct the sub contractor on an "hour by hour"
basis. You can only list things that are to be accomplished for the job to be done/accomplished properly.
And yes, if there is a small window of available time to do the job then you can give the subs these hours on this
specific job, but not in general or as a mandate for other jobs...
I suppose that State Laws could vary some, but I don't think by much. Remember that one of the things the States want is to collect withholding taxes from every paycheck and this does not happen in all cases with sub contractors. They pay quarterly (yeah) or at the end of the year when they receive their 1099's
I paid a lot of money directly to learn this lesson. We even hired 'expert attorneys' in addition to our own that were specialists in these matters.