Wow, I don't know how people can complete one mining run so fast. My mining Python is quite similar to yours -
https://s.orbis.zone/6ves The time it takes from reaching Borann triple hot spots to selling the LTDs in a station, takes me about 2.5 hours on average.
Apart from making sure that one hits the triple overlap, the crucial parts are how you mine and how you prospect. Prospecting is a major part of the mining game and if you can speed up your prospecting speed you can gain a lot of time. Key for this is not waiting too long for your prospectors to reach the target asteroids (and being in the triple overlap) so target relatively close asteroids whenever possible and fire off a new limpet as soon as you confirm that a prospected asteroid is not minable.
For the mining part, positioning and correct limpets vs lasers numbers are the most relevant. You want to position yourself such that the fragments form a steady stream coming in under your ship and preferably pass close to the cargo hatch. You want to be as close to the asteroid as you can. 5 limpets for 2 lasers is on the low side. If you have too few limpets, the limpets will not be able to keep up. This results in fragments being missed spreading out and it will then take the limpets much longer to pick them up. I made this mining run video some time ago:
The parts between the asteroids are fast forwarded (this is why I sound like Donald Duck), but you can see the positioning close to the asteroids and how the fragment stream is directed below the ship. (This is 7 collectors and 3 lasers.) This particular run I was rather lucky with the LTD content of the asteroids and filled up in just below 40 minutes of actual mining (but the sell station was quite far off so the run itself took 1h17min.
Without actually seeing you mine, it is difficult to say where the "problem" lies.