the kind of steps involved in true crypt are:
1. First u will have to create a kind of a locker which will be totally encrypted and u have the full liberty to choose the size of the locker. It means if u r going to create a locker of 8 gb it may take close to 20 mins (approx). Now the locker is ready.
2. now if u want to copy to/from this locker u will have to open it manually everytime by entering the password (and the keyfile if u have enable keyfile option). Opening is seconds job.
3. copying to and from is just like any other copying process, no additional time taken.
4. close the locker and it closes instantly.
So, it will take time only once in the begining when u create the locker thereafter its just as normal as any other copying process.
I hope this makes it clear.
njoy