From my perspective, basically it is the same between the entry is submitted publicly or by PM.
As we know, if the entry is submitted publicly most participants will submit it in the last hours even minutes.
There are some submission already but do not even think that those are the final entry from the participants.
The most important thing for this kind of contest is, try our best and do not try to think about other's submission as it may force us to play more and more in order to get better entry but it can make us lose more than what was planned.
Based on competition it is very different because we have experienced it from another contest before ambitions will increase if the entry is sent publicly
Say I have got the x500 multiplier when I post it, other users will search for x600 I will do the same thing when my multiplier is defeated so I will spend more time
When I posted it in the last hour then my competitor will have less time to hit but still luck and strategy are needed.