I would go back in time to mine bitcoin on its first year. That way, I would be able to amass a high number of coins and would lock tehm on a wallet back in time to access it in the future. Moreover, I would contribute like one of the early adopters and become known throughout history.
You do not need to go back to the past, instead, you can try to think of the future. Just like what @OP is trying to say, we can assume that the current year is the past year and the future of 12 years from now is the present. This mean, we do not need to have a time machine but instead, we can just start accumulating Bitcoin at the current price and wait until 3 halvings had passed and see for ourselves that we had made the right decision of accumulating Bitcoin 12 years ago(present year).
^ I would still love to go back fast if there is a chance, to be a part of the history probably. Being a Hal Fenny? a Pizza man? What else?
And ACCUMULATE since back then it is very cheap, I can probably hold 100 BTC or thousand of it as I want. But now, yes you can still accumulate but it needs also a big amount before you have a whole number of BTC, itis totally different.
However, we don't have that machine, so let us accept the fact that we are here now, all we have to do is just accumulate even though a small fraction so that we have a gain rewards in the future.