With MOC noms, there are no bonus points for turning them in super-early. So, take your time to do them well because, in many parts of the country, securing a nom is a huge part of the "battle." However, do NOT miss the deadline as, especially in super-competitive districts, that's an easy way to reduce the number of applications (tossing those submitted late).
Also as noted above, some MOCs have very early deadlines (one MOC in our area used to have a deadline of 15 SEP. School here didn't start until after Labor Day. So, if you need teacher recs, transcripts, etc from your school, you need to plan for that. Other MOCs may allow applications almost up to the last moment.
Finally, in many areas of the country, MOCs ask you to rank your SAs. In some areas, you may only be able to get one nom to one SA per MOC and in some areas the MOCs compare notes and you may only be able to get one nom period. There are many threads on this topic with some great advice. I won't rehash that here other than to say that you should give your selections A LOT of thought now so you aren't regretting an impulsive decision come winter/spring.