It will take about 3 months for the hormones to kick in to any degree. There will not be a magical cure to your dysphoria even if you do take the pills starting tomorrow. If you are over 18 as Grace said, then you call the shots and mom does not. You do not need her blessing or even approval. Waiting 90 days will have little effect overall though. Repeat, Hormones do not cure GD. There is value to longer term therapy but I can even see where a single session may be enough to start the hormones, keeping in mind that yes you can stop HRT if it is not doing what you demand of it. But the record is back to its scratched part and "hormones do not cure GD or even slow it up". I offer the experience of old age and having been on hormones for nearly 5 years. It does not even matter that I am post -op, the dysphoria is still sitting there laughing its head off at me, only thing to it, I laugh back now.
My kids are 40, 37 and 34, and by now I have learned when not to "daddy" them. It could be time for your mom to learn that though.