It depends on many factors.
- The bank; if it is Islamic or conventional.
- The L/C; it is cash L/C or credit L/C?
- The kind of amendment required: Is it simply extension of L/C expiry, extension of last date of shipment or change in requirement of documentation or is it an increase in the L/C value which may require further approval if it is credit L/C.? Normally, with proper documentation; it doesn't take more than three working days.