If your due date is the 20th they will be calling you on the 21st looking for a payment and charge and you a late fee
It's a card for people with bad credit, what else can I say. Approval was easy, make your first payment on time and you generally get an immediate credit line increase.
It's a tool to help build, or rebuilt credit, and should be used as such. The annual fee is high, the interest rate is high, but as a starter point it's been helping my credit grow ever since
I opened the account a year ago. Once your credit improves and you can get a better card, do it.