Note, given the behavior I saw, it's also possible that it was only behind by about 40 seconds, and the second screen update wasn't related to NTP or data from cell towers. The first (immediate) update could have been the usual split second before the screen redraws on resume. In any case, that's still losing 4 seconds per minute, which it shouldn't be doing. I think the usual tolerance is more like 0.5 seconds per hour, at most.
Note, given the behavior I saw, it's also possible that it was only behind by about 40 seconds, and the second screen update wasn't related to NTP or data from cell towers. The first (immediate) update could have been the usual split second before the screen redraws on resume. In any case, that's still losing 4 seconds per minute, which it shouldn't be doing. I think the usual tolerance is more like 0.5 seconds per hour, at most.