We gathered some of the greatest mathematical minds on MR and came up with the following:

There is a 99.7% probability that 4 users will get laid over the Vday weekend.

However, if we add the bed, subtract the clothes, divide the legs and pray you don't multiply - we can increase the chance of an unpaid sexual encounter with actual live females by a factor of 2 simply by moving our Vday competition to the following weekend.

So in interests purely of adult coital reasons, the MR Vday Massacre of 2015 will take place over a 24 hour period on Feb 21st through Feb 22nd.  The event will be broken down into multiple mini events, so a full 24 hour commitment is not needed to compete.