Configuration is stored in BBRAM only if yoy issue UBX-CFG-CFG to store config data to BBRAM. BBRAM persists only if V_BCKP is maintained.
Ephemeris stored in BBRAM expires in two to four hours. When ephemeris is expired, it will take 18 to 36 seconds to refresh it under good signal conditions.
AssistNow provides real or synthesized ephemeris depending upon which version of AssistNow you are using. This shortens TTFF to on the order of 10 seconds under good signal conditions.