6,741 is episode 4, but it was filmed after episode 6, perhaps to give Shaw more time to get back in fighting trim after giving birth to twins.
Who knows what the title refers to? If it represents days, 6741 adds up to about 18 years. If is represents hours, it's about 280 days. Is that how long Samaritan has been "alive" with government feeds?
Maybe that's how long Shaw was held in captivity? Maybe that's how long since Carter died, at least in Hollywood time? Or the amount of time since the finale in season 4 (YHWH) was aired (the gap between season 4 and 5 was long).
See article link provided in comment above, by Johnny Bones.