About this time each year I begin to get questions on when to stop irrigating cotton. Through the years I have recommended that growers evaluate the field when bolls begin to crack. If there is good soil moisture at this time, then this is a good time to stop. If not I would suggest one last irrigation to help finish the crop out. I would not push irrigation past 10% open boll or you will begin to chance the start of hard lock and boll rot.
The UGA Cotton Irrigation Scheduling chart suggest that once you get to the 7th week of bloom, start backing off to 1 inch or less per week and consider stopping shortly after.
I did see one exception to this several years back when we were growing DP 555 and we had a small bottom crop and a very heavy top crop, and temperatures at 100 degrees. In that case, it was wise to continue irrigating past 10% open bolls. I would evaluate the bottom crop, top crop load, and weather forecast to determine the high temperatures if considering going past 10% open boll.