I think it would be really useful to add posibility to mark some days of week as your day-off, and don't include them into deadline. Like, if my day off is sunday and project's deadline is 7 days, then it should be finished in 8 days but technicaly in 7 working days. Cause sometimes it is pretty hard to explaine the customer that i won't reply for example tomorrow, because i cannot work whole month wihout weekends so i include it in deadline.