Can you wear the vest overnight? If not what is the maximum time you may wear it?

You can wear the vest for as long as it is comfortable for you, including overnight.

Just be sure to use only the lowest temperature settings (not more than 40-45 degrees celsius) if you use it overnight.
If the PEMF function relaxes you, you may choose to cycle it during night sessions. But if it works stimulating and activating for you, it may be better to use only one PEMF or Photon procedure before sleeping.