I am a game/AI developer / ML researcher, this was just passion project of mine and it was... tens of hours, I do not have the exact numbers. But the biggest setback, which took most of the time, was the audio issues, I thought all the time that my audio backend code is wrong, but it was Watch speaker not liking low freq noise. This on itself could take cca 10-20 hours, I have tried a lot of things before realizing the above mentioned fact.