By default, the ps command in Linux is the date on which a process was launched. But it does not specify the hour. To obtain this information, it is necessary to use several options described in the manual.
And here is the command to use to get the start time of a process (here we want the information to the messenger Pidgin):
# ps -e -o pid,comm,lstart | grep pidgin
23666 pidgin Mon Nov 3 08:22:58 2010
Ps normal on this same process would have given this:
# ps awwux | grep pidgin
sic 23666 0.0 2.3 99256 48908 ? S Nov03 3:24 pidgin