Regarding GPS receiver date determination: 1. The GPS navigation message is 12.5 minutes long. A receiver should resolve UTC correctly within 12.5 minutes. See ICD-GPS-200 (publicly released).
2. Virtually all receivers can correctly resolve date (and will do so quickly), given an initialization "seed" date that is within about +/- 512 weeks of true date. The receiver will adjust date forward or backward based on this seed date, the 10-bit GPS Week Number (WN), and GPS time-of-week (TOW) (i.e., day of week) transmitted by the satellites. 3. As has been pointed out, some receivers also implement a clever hack to determine date that looks at UTC Leap Second (LS) value, and chooses a date based on WN, TOW, and LS. That is, the receiver implements a sliding 1024-week window whose limits are determined by the current value of LS. Current date "will" then reside within this 1024-week window. 4. A receiver may be at risk for needing a software update if its authors picked too small a value to associate with each LS increment, and if Mother Nature doesn't cooperate and slow the earth's rotation at something close to the mean rate. I note that the interval between the last LS increment and the next one will be 7 years. --Tem
