According to the ATF rules, a multiple firearm sale needs to be reported based on "business days". So we need to know what days you are open for business.
If you sell or dispose of more than one handgun to any non-licensee during a period of 5 consecutive business days, the sale must be reported on ATF Form 3310.4, Report of Multiple Sale or Other Disposition of Pistols and Revolvers, not later than the close of the business day on which you sold or disposed of the second handgun. The licensee must forward a copy of the Form 3310.4 to the ATF office specified thereon, and another copy must be forwarded to the State police or local law enforcement agency where the sale occurred. A copy of the Form 3310.4 also must be attached to the firearms transaction record, ATF Form 4473, documenting the sale or disposition of the second handgun.