sbws: use at least 4 measurements that are at least 6 hours apart
Split off #27346 (moved):
use at least 4 measurements that are at least 6 hours apart, because:
- there is a daily cycle
- each day contains 2 similar points in the cycle (it is an up and down cycle)
- if all 4 measurements happen within a few hours, they will still be biased towards that point in the cycle