Free Throw/Subs/Time out.

[Chess Ref]

Players Lined up for 2 free throws, coach requests time out, granted. Subs at the table. The question can these subs enter the game at that point or do they still need to wait for the first free-throw ?

I let them in because well cause it occurred to me that I didn't know what the procedure should be and it just seened intuitive to allow them in . Was I correct ?