A forum at webmaster world mentions that of late Google SERPs have started to cache time and date of the webpage when you last visited.
This new feature however has not affected all as tedster informs :
"No times for me, just dates. I'm currently seeing results from these IPs 22.214.171.124, 126.96.36.199, 188.8.131.52, 184.108.40.206 ." Thread at webmaster world.