Help with deciding on when to buy an upgrade versus rely on wait list on domestic flight

I am 1k and have flight from IAH to Washington DC on Sunday.

I applied 10k miles to place myself on upgrade wait list. I am number 2 and there are 2 open seats in business.

When do these clear and thoughts on likelihood? The cost for immediate upgrade is $250 and I would do it but worried I may need to change time of flight and so would lose that money.