I have some new information, when I get ungrounded I'll show the results and stuff, but for now just believe me.
13 seconds -- The amount of time a C4 remains stuck to an opponent when stuck, NO MATTER WHAT THEY DO, they can jump, attack, run around, do nothing, doesn't matter.
Til Explosion -- If you and your opponent keep resticking eachother, the 13 second timer resets itself. The C4 will remain transferring and sticking between the two (within 13 seconds) and eventually blow up after the 26.5 (explanation coming soon) seconds of the C4 timer.
C4 Timer is 26.5, NOT 27. -- I retested this when I found that the stick seemed to last 13.25 seconds (I rounded to 13 to be more practical since .25 seconds is almost neglible) and retested my c4 timer. It turns out it would blow up at around 26.5 seconds later, NOT a full 27 seconds. (started at around xx:xx:00 and it would end at xx:43:50, NOT xx:43:00.... so my first testing was wrong.
1.5 or 2 seconds (to hard to be exact) before a c4 can transfer from one player to another. This includes after a stick, and after a transfer. So you cannot immediatly transfer the c4 to an opponent, you must wait roughly 2 seconds.
I also have a few more things I'll be testing, but first comes some Link testing.