The upgrade should clear immediately you request it, if there is availability in the NC bucket on the flight - to check this, sign on, start the process of booking an award on the same flights checking "standard" award and not "saver" award, when the flights are listed mouse over the flight information, and if it shows NC is >0 the upgrade should clear immediately. Doing this means you can effectively pick flights that have upgrade availability if you have flexibility. If NC is 0 you will go onto the waitlist - and then there are rules in the run up to departure date for UA clearing (or not!) the WL which depends on passenger status, etc, that others will be better able to explain than I can.

Andy