On their first day, they will get a lot of accounts, if they syphon data and m set up backdoors quickly, one day could be enough to cause a good chunk of the damage.
Saddens me a bit. I like to trust hires and give them pretty wide access to everything. For my own company, I've so far only hired people I worked with in the past, but when hiring strangers remotely, I'll probably have to rethink my trust-first model.