Overheads mismatch between NEOexchange and ObsPortal/scheduler

[talister]

Scheduling 3I observations recently resulted in a mismatch between the NEOx input block length and the scheduler-calculated value reported in the Obs Portal:

• NEOx: 41 minutes (22x60s), scheduler: 2108s = 35.1 minutes
• NEOx: 40 minutes (21x60s), scheduler: 2017s = 33.6 minutes