I have the Austria Typhoon pack installed (in P3D) and I want to have the planes do a few TNG's. Is this how a TNG would be in the plan?

LOXZ,4/08:58:46,TNG4/09:20:55,140,F,9624,LOWL,4/13:36:51,TNG4/13:59:00,120,F,9624,LOWS,5/07:48:17,TNG5/08:12:53,180,F,9624,LOWI

Originally this part of the plan would not have a TNG in it. Do I need to change the times at all?

Yes you need to alter the plans to avoid issues.

Take the first leg as an example LOXZ-LOWL.
This is one leg. Simple.
However when you add a TNG you need two legs.
LOXZ-LOWL and LOWL-LOWL.

Also the leg following a TNG leg MUST begin at least 1 min and no more than 5 minsafter the TNG ends.
The MAIW standard is to set the difference to 3 mins to avoid compiling issues.

Thanks Steve.