Flight Instructor with student reported a low altitude event while maneuvering into a non-towered airport traffic pattern during a night training flight.

Narrative

My student and I were on a night VFR XC (ZZZ1-ZZZ1 via ZZZ2)He needed to fulfil some extra night hours for his commercial requirements so we stopped by ZZZ airport on the way back for a touch and go.Whilst on a long final for Runway XX at ZZZ my student was far too high so; since there was no traffic in the area; I advised we spiral down to an altitude from which we could make a stablised approach.After one 360 turn the VASI was still showing two white lights so I said to do another turn. Halfway through the second turn I realised our height AGL over our specific location was quite low so I told him to power up and continue on the approach. We were still on glide path referencing the VASI; but I fear we may have descended below 1000 AGL; and since we were over a congested area it's possible we temporarily did not meet the requirements of 91.119. In the future I believe I need to have an awareness of our height AGL whilst at low altitudes during an approach to ensure I meet the requirements of 91.119; especially given that at night your sense of height can be distorted.