LST

I'm not sure there is a "normal" with autos. It will begin flowering whenever its internal timer goes off - whether it does so on its own or because of something else that triggered it. For instance, I counted my 3rd week of my first grow as "veg" simply because I didn't recognize pre-flowers for what they were right away, and I call the week (whether veg or flower) based on how it begins the week. I think my first grow began showing pre-flowers around day 20 - only a couple days after yours, though i didn't recognize them for what they were at the time. This grow, there was no sign of pre-flowers with the same strain, light, and tent, by day 26 and I thought it might be because I was growing in a bigger pot (3 vs 2 gallon). But when I lowered the light 2" on day 27, pre-flowers appeared a couple hours later. So it isn't unusual with autoflowers and I wouldn't be concerned about it. As to LST, there's really no "rules" once you've begun it as, done right, the only stress is beneficial and minimal (it does not stall or pause growth like other training methods can), so you only need to wait until you have enough growth on the new node to properly tie it down - if you do, its grown enough; if you don't, it hasn't. I LST early (I started this plant at 3 nodes and 5" in height) and continue LST until the stems become too wooden to train.