Try our Train Search to find out trains from New Delhi to Aligarh.
Some night trains between the two places are:
Brahmaputra Mail (Departs from Delhi at 11:30 PM)
Farakka Express (Departs from Delhi at 9: 50 PM)
Kalindi Express (Departs from Delhi at 10:00 PM)
On the results page of the Train search, you can also use the filter on your left hand side, to specify the departure time window.
Hope this helps! Further, you can also consider taking New Delhi to Aligarh cabs, as the distance is not a lot and you can cover it comfortably via the road journey.