The Exchange Sacrifice
Maybe just take a better look before these sacrifices, to see if it is really worth it?
And maybe practice your opening more if your running out of time, so you can have the opening done win ten seconds, without having to think about it.
My sacrifices are fine, and I uphold an advantageous position throughout the game. I will attempt to take less time in my openings as you say.
But I okay some people, and it takes them about 30 seconds to do their opening. For me it's instinctive, and takes 5-10 seconds.
But about which opening? Sorry... I don't know.
Perhaps the reason your not winning is because whilst you can give yourself an advantage, you can't exploit it? To get over that things like tactics, strategy games would be good, and keep playing 10 min and above games, which will Help your tactics and strategy more, as you can actually think more about the moves.

The Greek Gift is one sacrifice I am aware of and have won many games utilising. However, this forum is mainly about the exchange sacrifice. Needless to say, your example of the London system is very helpful.

You are losing on time, not on the sacrifice, so you have to address the time problem. Any sacrifice is made so that you will have a short-term material superiority on part of the board and over control of key squares. "Short-term" means that if you don't have tactics that are going to pay-back that sacrifice with a mate or material gain over the next several moves or a clearly permanent bad position for your opponent, that was a bad sacrifice. For example, you don't sac a R for "well-placed N" just to get the N off the board - you need to get a quick pay-back for the sac.
In my cases, the knight was easily better than the rook, and most times I get a pawn for the exchange, as well as virtually no counterplay for my opponent.