If i want to top above 4th node ,

If it is an auto, I would not top at all, only LST. If it is a photperiod plant, you can top at any time. Topping at the 4th node should be done once you can cut there safely, no need to let the 5th node get too advanced. Agree with 0011011......get rid of the first 2 branches, the absolute lowest ones that sprout from the first true leaf.........they never amount to anything much.

I top it anytime its over 3 nodes.

"They" say to wait for 6-7 nodes before topping. this ensures a healthy rootzonea nd mature-enough plant that can handle it with little to no worry about shocking it. This 'they' extends beyond this niche hobby plant, too. Is it going to stall out if you cut before that? probably not but eventually you will run into aplant that gets impacted negatively at some point. not a problem in a small gardne but becomes more ofa problem ifrelying on a plan for many plants and lack of consistency can be a real concern. I never count the lowest 2 branches. They always seem to be weak even if they are trained to remain level with the canopy. i could be wrong about that. I prune them off as soon as i can safely get the friskars around the base of the stem without causing additional damage, lol. When it comes to lst or topping.. have a plan. Just doing it whimsically is a useless non-value-added behaviour. Have a target for your end canopy and work backward from there to form a systematic plant to get there... this will avoid wasted growth and over-crowding (assuming proper end goal). anything that requires a bunch of defoliation or wasted growth is self-inflicted madness. I'd want to know why it's so droopy first... if this picture was taken after ligths out, that would exaplin it... if it looks like this while the lights are on, it may be a problem worth fixing before you start cutting up your plant. If it only happens the last couplehours, could be from too muchlight. If it's happening after an irrigation, it's a poorly constituted medium and you should increase the amount of perlite or similar for better drainage/aeration in future. if happening all the time, probably some problems brewing in rootzone -- overwatering or pests chewing on roots etc. make sure it's healthy before doing stressful things like cutting the plant. just in case... 1) fully satureate 2) wait for appropriate dryback and repeat. If over-complicating this simply irrigation process, stop doing that. None of this should cause a problem. if a problem is seen it is due to a poorly constituted medium or you aren't following the basic instructions. Don't choose a volume to give. you give the volume necessary to accomplish the tast - full stop. If this is soilless, relgiously get 10% runoff waste water out the bottom, too... and don't let it sit in its piss, regardless of growing method. A little runoff is find to ensure full saturaton in a soil. runoff for a soilless context ensures the fertilizer provided does not build up in the pot.