The Timing Advance Command in RAR takes 11 bits and it can indicate an index value TA (0, 1, 2… 1282) which used to control the amount of timing adjustment that UE has to apply. The amount of the time alignment is given by NTA = TA × 16. The Timing Advance obtained via RAR is always positive
If TA = 1 ⇨ Timing Adjustment = NTA = 16 Ts = 16/30720000 sec = 0.5208 μs
So ue will start UL transmission is same subframe with .5208 μs before so that it should reach at enb in same subframe boundaries.