You, sir, are quick!
I don't see any problem allowing hourglasses to work. The whole strategy behind fighting a mono/duo Time deck (as opposed to a time-based rainbow) has always been to delay getting set up in order to avoid the dreaded Rewind. If you're already doing that, you can be cautious about your setup and possibly provoke one or two of these, then play creatures during the effect. Remember the opponent can play stuff too.