The newly bought Yadea TDR740Z changed from red to green after 2.5 hours of first charging. Does this mean that it is fully charged?

Yes, if the battery chargers are all regular products and are original, once the red light jumps to the green light during charging, it means that the battery charging is coming to an end and the charging state is in a trickle charging state. You can unplug the charger anytime and anywhere, and don't continue charging for many hours. That's the old yellow calendar.