once you're undergrad school uploads your letters onto VE, it is accessible instantaneously to your designated med schools. VE is essentially an online repository of your letters - your undergrad school uploads them in pdf format, your designated schools can download the pdf whenever they want. The time it takes depends on the med school. Some med schools I applied to downloaded it the day I submitted the secondary. Some have yet to download it weeks after. But it's always there for them to download when they feel like it.