Sorry to be a pedant, but it's LOSE height.
In an unpressurised aircraft I use time-based parameters. This allows me to plan on a RoD of 500fpm which is comfortable for passengers. So if I'm at 10,000ft and I need to allow 20mins to descend to sea level. I usually add a minute or two to allow for the speed increase in the descent. So, assuming no level restrictions, I'll be requesting descent from FL100 22 mins before destination.