As a motivational aide, the figure below is a record of the number of abstracts created leading up the the abstract submission deadline for ICT2014. The vast majority of abstracts were drafted and submitted in a single website session very near the deadline.
Consider the conference organizers. They have little idea of the actual conference turnout, or even if the website and review process can handle the load, until the crush of submssions begins in earnest perhaps two weeks before the abstract deadline. Quite often, as happened for ICT2014, the organizers will elect to extend the abstract deadline somewhat. This gives them some limited ability to manage the number of submissions, but authors should not count on the deadline being extended.
The author too faces a challenge, of course. They naturally want their abstract to reflect their most recent results and may work until as close to the deadline as practical. No system can perfectly balance these opposing factors, but perhaps having some data like this may aid in your planning.