The advance fares aren't out yet for the 11th.
Getting the TP 50% discount can be a bit problematic.
To get the complete list of available services you will need to book as two singles.
The outward shouldn't be a problem, but the return is difficult to get to because it's usually a bit quicker to take a Northern service from Manchester.
Anyway, go through the student 50% off link, put in your return date and say 'after 15:00', and you should get the option of the 15:40.
Now you can click on the 'Click here to check if slower routes with cheaper tickets are available.' at the bottom.
Now click on the topmost 'check for trains button' and you can move through the available times to find one that suits you.
I tried this for 3rd / 4th, it's no problem getting a return for £13.30.