What can be done will depend to some extent, what your Chairman has done or is doing that agrieves you. As a rule of thumb, a council chairman is entitled to remain in post until the next agm. He need not resign even following a carried no confidence vote. If changing the chairman is considered to be the best way forward by the majority of council it may well be that a quiet word from someone respected by the chairman might do the trick. If having a quiet word is what you propose to ask your clerk to do, there are no time constraints. However if you are asking the clerk to agenda an item relating to the conduct of your chairman, you need to get it to the clerk sufficiently early so that the clerk can include it in the summons for the next meeting.