BTL, my only reasoning for that is to not put pressure on anyone to get it done within a certain time frame. Three month builds might not appeal to everyone. Neither do, maybe year long builds, but I'm just messing.
How those builders get those 48 hour builds done is besides me. FSM years ago, had stated it takes about 20-30 to complete the average model kit. I suppose. Mine are spread across several millennia, but under 50 hours.
Not that this build would take preference over anything one your bench. It's just a hobby.
ScaleMates, if I may mention them here, have several every year that go from a couple months to some currently to the end of the year.
You want to participate in a SBD Daultless build if that is the only group build, you have till December to finish it.