I start my master's year project in mid November this year and am currently applying to graduate school, most of whose deadlines are 1st of December. I was wondering if it was acceptable to ask my master's year supervisor for a letter of recommendation despite not having actually started in the lab yet? For more context, we have interacted twice in person and over video and have been communicating over email. But as a research lab degree I was wondering if it would be too soon to ask my supervisor for a letter, but at the same time wouldn't it appear odd that I haven't submitted a letter from my supervisor for my graduate school applications, especially considering my masters field is very closely linked to what I wish to pursue in graduate school. Also, when would be the best time to ask - once I start in the lab mid Nov for a 1st Dec deadline or just before starting, giving them a bit more time?
EDIT: I'm doing a Master's in the UK and applying to US graduate schools