Ah, see I was super into politics as a lib, so I know exactly what it is. (Fair warning: this only makes it more irritating.)

Basically, campaigns are required to submit fundraising data to the FEC every quarter, and presidential campaigns with fundraising over a certain amount have to file monthly reports. There's no actual deadline from the donor's perspective; it's just about pumping up the numbers in advance of the filing deadline so the campaign looks stronger.