I've just taken a look at the documentation for those formula fields, but the dates I'm using are all in the future. The formula is for a worktime on and off schedule for many weeks until the end of next year. I'm not seeing how TONOW of FROMNOW are going to help me there.
I don’t know if TONOW() or FROMNOW() give a specific number of weeks, but I do recall that it gave a very human readable duration including varying units. I am away from a computer so I cannot test it.
it is possible to craft a formula that says the number of weeks and days, but it would not be a simple one function formula like TONOW() or FROMNOW(). If you want to experiment with crafting a formula with the exact output you want, look into combining both the quotient and the remainder when you divide the number of days by seven.