Yes, the mantra method is very time consuming. But it’s then also very gentle and usually very safe and easy on the energy system, building it nice and slowly with no rush, no stress.
I don’t know about yoga, but in qigong there’s visualizations and breathing to draw in more energy from the cosmos and build qi faster - it’s called “cultivating qi”. I think you can use your breath and direction via your mind with the mantras in a similar way.
So you could say, while you’re doing the mantra breathe in and pull energy, then breathe out and see that energy retained and consolidated into your root wheel (chakra) or whichever wheel you’re wanting to develop more.
This would be adapted from techniques in posts like this one: