There are no limitations on using the personal dev instances as long as you log in every 14 or so days.   You get a notification if you start to come up to the time limit without logging in.   Otherwise, it's yours to use as you please.

In the past I've also seen ServiceNow provision an instance, temporarily, for companies that were interested in the product.   I am not sure if they continue to do this since the developer instances are available.