Is it possible to hide hrt from parents?

Hi, im 16. Let me start by saying I've been out as transgender for 4 years, and have been using a different name and pronouns for those 4 years, in all social situations, school, work, etc. My parents are supportive in the way that they use my preffered name, and sometimes my preffered pronouns. They don't have an issue with me being trans, but they have an issue with me being a boy, in the way that they do not support any sort of hrt, and they think i will regret it, and want children some day, and they also think it will give me cancer.

Dysphoria is driving me insane though. My mental health has been horrible for years, but this year I got it way more under control. I've gotten diagnosed as autistic and I've been on prozac for over a year now. So im actually doing good. but dysphoria is just throwing all that down the hill, really.

With the genderGP service, if they deem me fit to consent to treatment, I can go on testosterone without my parents knowlege. I know I'll go on it when im 18 anyway, and I've told my parents this too, but it pains me to have to wait. I've been asking for hrt for about 2 or 3 years. I know I'll have to hide it.

Is it possible to hide the effects? how quickly do you start to see a change?