More of a "For Your Information" than a guide as the achievement is rather self explanatory.
To confirm that the following did not affect this achievement for me:
1) You can amend the system date manually, playing offline.
2) You can amend your training days mid program.
* I missed a day due to visiting relatives so I disconnected the Xbox from my router and signed in offline so I could amend the date back and catch up on the session I'd missed.
Initially I'd picked three training days a week but amended it to two mid program.
EDIT: A couple of good points raised in the comments...
You have to do the exact dates the program specifies and you need to do them in order so be cautious if you're amending the system date.