Hi mate
Some details about your set-up would be nice, so we can tailor the advice accordingly.
I'll assume it's relatively high-energy by your plant selection...
It's usually best to leave the first trim for at least a couple of weeks - much longer if you're not injecting CO2. This gives the plants a chance to build some nutrient reserves and put healthy roots down. Then when you do trim, the new growth will be healthy and the pruning won't stress the plant.
I prefer to prune my plants during the weekly maintenance session, at the start. Then removal of the cuttings can be done in conjunction with the water change. It's best to do a water change before the photoperiod starts, otherwise the CO2 fluctuation may trigger algae.
Once the glosso and HC are well-established carpets (usually after about 6-8 weeks) you can trim almost right down to the substrate. From an aquascaping perspective I like to trim right down nearest the glass and let the plants taper upwards/rearwards, as this adds a sense of depth. I don't like to see a mass of carpeting plants up against the front glass, but it's a personal choice. Before this 6-8 week (or whatever it takes) you can selectively trim and re-plant to encourage greater coverage.
The Rotala needs to be treated like most other stems. Every time you trim it, two new shoots will grow from the node. Repeating this process can give you a really bushy appearance, but the lower portion look ugly as they become starved of light. So you need to plan your first trim 'site' with this in mind.
Here's a good article by some Japanese newbie about trimming...
Trimming to Refine the Nature Aquarium | Details | Articles | TFH Magazine®
Have fun!
George
