As an add-on to what Snellasia said...
If you prefer using the time-changing method, you have to set the clock one minute before each time. Every two times you use its training call bonding, the bonding percentage will go up 10%.
If you use the bonding items (Unchi-Kun Sub, textbook, campfire, boombox, etc.) 34 times, your bonding percentage will go up 10%. You have to use the bonding items a total 0f 340 times to get 100% bonding.
Also, playing the games with the parents a few times won't do anything. You have to play the games a lot to raise your bonding percentage up by 10%. And I mean a lot.
Hope I helped!