they will show the same time when the time difference between them is 12hours( Why 12 hours? you can get it from the question as we have 12 hours in a table clock and wall clock )
taking the difference from both clock:--
=>2 + 4+ 6 +8..................= 12 * 60 mins
(as one clock looses 3,6,9....... and other 5,10,15...............)
=>2(1+2+3+................k) = 720
=>2(k(k+1)/2)=720
=>k2+k-720=0 (solving eqn we get)
=> k= 26.3374738 hours answer
so after 26.3374 hours it will show the same time.
which means 10pm + 26.3374738 hrs = 10pm +24+ 2.3374738 hr
=10pm+2hr + .3374738 hr(.33774738*60 min)
=12pm + 20 min + .24842804 min( .24842804*60 sec)
=12:20:14:9056823 sec.
so it shows corect timing at 12:20:14:9056823 answer.. :p