There´s something that happens each month to most of the bill paying public, we send more money out the last two weeks of the month than the first two. Rent, mortgage, utilities, etc. overwhelmingly fall due at the end of the month.
Depending on your product or service, you may not want your invoice competing with mortgages in the fight to receive your customer´s money. A better choice may be to compete for payment earlier in the month, being paid from the first month´s paycheck, not the second.
Something I like to do is stagger my receivables, with some invoices payable in the first two weeks of the month. This levels the flow of money into my business, making it easier to budget and pay personal and professional invoices of my own.
It´s something you ought to play with a bit. Staggering invoice due dates may not only even your flow of income, but you may find it has a positive impact on your operations, reducing the wave of back office activity to bill customers.
Experiment with small groups of invoices, find what works best for your market, and then move your operations to what contributes to the betterment of your business.
Food for thought.