Exceed means TO GO OVER certain limit set ( time, money,weight) Your luggage can not exceed 20kg ( has to be under 20 kg) You have exceeded your £500 credit card limit. ( you spent over £500) Hope that helps

It depends on what shouldn't exceed four to six months, lets say that you are building a house or finishing a project, obviously doing that in 3 months would be better, so it really depends on the context.