Plankton,
like tux-pinguin is trying to tell you: we can't help you with saying where or when you should exactly level. There are just too many diffrence between chars and playstyle to tell. So basically your question is a bit absurd: levelling is completely personal!
It's all up to you to find out what your char can handle. So go in the chantra world slay a mob without any buffs and if your char can handle it without problems, you know he can bot there. Just make sure he has enough pots and you can go out and have some fun with your friends while your char is training. You probably won't be in possesion of the chinese bot, so you will be slaying most of the time one mob at the time. So take your skills in function of that! High defense (skill block, health, etc), good one on one attack, and good armor with the normal stones (hp, phys def and phys rest) afre essential. If you do this you will able to let him bot above his level, and in dungeons without probs.
You will hit the 40's without problem with this method in no time. But like tux said it's trial and error. See for yourself what the best way is. This is one suggestion but there are lots of others to try.
So enjoy archlord,
cya
