My wife and I were first time surfers and our instructor Alexa managed to get us both to stand up on the board within two hours of a semi-private lesson. My wife made it on the first wave and I also managed to surf a wave at the end of the lesson.
For me it would have been better to do some warm-up exercises on the beach and maybe also have a few more minutes of instructions on land. Nevertheless, my wife proved that this wasnāt really necessary... at least for her.
Be aware that the harder part of learning to surf is not to stand up on the board, but to paddle out to where the waves break. Apply good sunscreen before and prepare for some muscle ache :-)