Its not about negative/positive. There can be many things: equipment availability/condition, weather condition, support of locals, disturbance by unsocial elements, fund allottment etc etc. They have to keep everything in mind. Maybe the time takenis more but they are doing this to be on the safe side. If the project will be delayed (high chances even now) then sometimes judiciary gets involved too. So not to take any untoward risk they ask for more time.