If someone recently bought the house I'm living in, how long is the new owner required to give me to vacate the premises?
Under federal law to help renters in your situation (it's calld the "Saving our homes act" or something similar), if you do not have a written lease or have a written month to month lease, you required to leave in 90 days.
If you have a written lease for a defined term (e.g. a one-year lease), then if the home is bought as an investment property, you get the longer of 90 days or the remaining lease term. If the home is bought by someone who intends to live there, you get 90 days.
The buyer can, of course, agree to give you more time or to keep renting to you.