To have some idea about the possible time span, we can estimate some "typical" flight frequency and length: if the average flight is 2.5 hours there, and if the pilot flights both to the destination and back in the same day (which is reasonable to expect) 6000 hours means 1200 flights to the destination and back, and if only one such is done per day (with the times on the ground it's surely more than 8 hours) then assuming 4 of such per week and 48 working weeks per year, that gives 6.5 years for the pilot and 5.2 years for the co-pilot.
Bhavye Suneja, the pilot - Suneja had logged more than 6,000 flight hours, according to Lion Air.
His co-pilot, whose name was Harvino - Harvino had logged more than 5,000 flight hours, according to Lion Air, which named him alongside Suneja.
https://www.businessinsider.com.au/lion-air-plane-crash-vict...