It is almost impossible for expats to open bank accounts in Libya. Most foreigners have their salary paid into an off-shore account.
It is slightly worrying that the employer has said it will take 3 months so ask them exactly when you will expect to start work and where your money will be paid till the account is sorted. With any job offer you should not be paying any more to the employer or having them back-date your pay.
Read the Banking, Money and Taxes in Libya page for more information.