Sure, you can add such a condition, but I'm not sure how checking for hours of uptime will prevent the loop.  That is, if the router reloads (for any reason), and when it comes back, the host in question is not reachable, then the router will still continue to reload.  What you might want instead is this to use nesting.  For example:

event manager environment quote "
!
event manager applet track-up
 event track 100 state up
 action 1.0 cli command "enable"
 action 2.0 cli command "config t"
 action 3.0 cli command "event manager applet track-down"
 action 4.0 cli command "event track 100 state down"
 action 5.0 cli command "action 1.0 syslog msg $quote Ping has failed, reloading the router$quote"
 action 6.0 cli command "action 2.0 reload"
 action 7.0 cli command "end"
!
event manager applet remove-track-down
 event syslog pattern "SYS-5-RESTART"
 action 1.0 cli command "enable"
 action 2.0 cli command "config t"
 action 3.0 cli command "no event manager applet track-down"
 action 4.0 cli command "end"

Using these policies, you will only see the reload if the track had been up.  On a reload, the track-down applet (if it still exists) will be removed.