How long of a time period does a company have to send you a bill?

I am currently living on base housing and they have decided they were going to start billing us for our utilities. The company, ista, is six months behind on send us our bills. We will recieve a bill due this month, but the time period for untilities used was for six months ago? Is that legal?|||It's not good form, but it's also not illegal. If your jurisdiction has a statute of limitations and if it is for three years, then they could wait for 2 years, 11 months and 29 days before they send you a bill and it would still be legal. But the company is demonstrating bad business practices. A good business will send out bills as soon as possible to get paid and follow up on dead beats.|||it's legal and you'll probably get a huge bill.