Next to flight time, hover over the ? and you'll see the different components that make up the block time. Couple considerations -
1. The 737-Jurrassics (100/200/200Adv) are set with very slow cruise speeds in the game, thus, their flight time will be 30-45 minutes longer than say, an A320, 727, etc on a ~2000nm route.
2. Going westbound (for BOS-LAS) you'll encounter a headwind. This is more pronounced in real life in the winter time where for transcons, the westbound block time is typically an hour longer than the eastbound block on a round trip due to the winter jetstream/winds. The difference is much less prnounced in the summer.
3. For BOS-PNS, it will probably compute to about 3 hours of flight time + 30 minutes of taxi time. A quick look at a jet blue average in-air times for BOS-FLL shows they average just under 3 hours airborne...