They must be kept in good order showing the exchange transactions you make. If, when you leave the country, your form is irregular you may be fined heavily or have your valuables confiscated. Credit cards are rarely accepted. French Francs and US Dollars and to a lesser extent, Pounds Sterling are readily accepted. Mon to Thurs.
Some banks close for lunch.
During Ramadan hours are shorter. All Internal flights have to be paid for in Algerian dinars and you may will need to show your currency exchange form to purchase a ticket. In most cases you need to book your seat well in advance of your intended flight. You may have to book a few days in advance if you want to get to Tamanrasset. But when the situation improves and Algeria once again become a safe place for travellers, it will be possible if you plan on travelling further south into Niger, to hitch a ride with another overlander in Tamanrasset provided you're prepared to wait around a few days.