Most college application deadlines occur between October and February. Students often wait until close to published deadlines to begin college applications probably thinking "how long could it take?" The answer is that it is likely to take several hours depending upon the application. Some students spend days on one application because they don't have all the answers at hand.
Answers to some questions on college applications involve information only parents have and they often have to look up those answers. The questions that students must answer involve reconstructing all their activities in each grade. Most students have to think about those questions to make sure they list everything. Essays, critical to college applications, take time. Hastily written essays hurt chances for admission.
The best approach to completing college applications is to develop a calendar for every task involved with a target date for completion well before the final deadline.
Applying for college admission is an unforgiving process. If you miss a deadline, colleges don't usually make exceptions.