Moran,
I would say, we should not compare the ping results between a pc connected wired & wireless, there are lot of difference in the way they get access to the medium to send the data.
Moreover the heartbeat is originated from the AP, so doing a ping test from a client behind the AP is different.
Regarding the incorrect time for the heartbeat alarm, this needs some more data, to find the root cause of this. Could you please go ahead and open a support case, so that we can provide you the steps to collect the required data in finding the reason for this issue.