My observations on this and altar has been it makes no difference if u enchant several times in a row or if u space it out. Totally anecdotal I realise. I did a session yesterday of about a dozen enchantment and while I had a couple of failures...I had no resets. Personally, I never try to go above level 4 unless i have enough inferno and aqua to get back to level 4 if there is a reset. That way the pain is not so great.