When should i top the plant?

now can be a good moment

You're not shooting pistils yet, you probably could still but I wouldn't wait any longer. Week 2 woulda been safer.

When it comes to plant training, you need to work backward from your intended canopy size and number of colas or it's purely whimsical when/if you top. Have a goal. Work toward it. It makes the decisions automatic. 4-8-16? or 6-12-24? Start with 4-6 branches and go from there. If filling 4 sq ft, probably want 8-12 colas depending on genetics. ahh shit.. it's an autoflower? Train it.. don't cut it. Can you top? sure but it's less effective for an autoflower. Break apical dominance with any taller growth tip until the rest catchest up, then release it... continue to do little maintenance to keep canopy even as you go. Something outpaces other stuff, bend it down for a day or two. Just weakening the top portion of branch 1-2x a day can be enough if it's a small deviation in growth... maybe you just do that in the morning for afew days in a row etc... more extreme growth differences need a bit more substantive response.

Now... if it as a photoperiod. but its also an automatic so maybe not top it and just use some LST. Could also back off your light and bit and encourage some inter-node stretching a bit. gives yea more room to work with.