You can adapt one school's essays to another school, but trying to force it in there is a bad idea and the adcom will likely notice that it's a recycled essay. While the essay prompts may be similar, you'll see slight nuances that distinguish exactly what they're asking for--for example, one school might ask why you want an MBA, while another will explicitly ask why you want an MBA
from this program and how this school will help you reach your goals.
Plus varying word lengths are almost a given--there's a big difference between a 500 word career goals essay and a 1,000 word career goals essay. You need to make sure each essay fits for that particular school--that you've done your homework, read up on programs, studied employment reports, talked to current students, etc. to show why you think that school is a good fit for what you want to do.
If you don't have time to spend on putting together good essays, then you really shouldn't be submitting an application in the first place...there's no way around that. Aside from your essays and chasing down recommenders, there aren't many time-consuming things on the applications.