Crawl is already very good on cutting down the tedium (autoexplore etc). Autoattack (tab key) on weak stuff helps.
My favourite options bit, probably called 'edit options/rc' on cao, is 4-g:
travel_delay = -1 (default 20)
explore_delay = 5 (default 20)
Play around with these values, travel at -1 won't show your travels at all (so it's just ctrl + g, ..., arrival)
explore at 5 was lowest where I could still get what's going on onscreen (blind autoexplore at -1 made me slower if anything)
Waypoints help if you're leaving an area you'll come back later to.
CTRL+w, numbers to set waypoints, CTRL+g, numbers to visit the waypoints.
Macros help. click ~, then m for the macro making menu.
Macros I use often are are ff (throw whatevers available), cey (chop/eat/confirm), za, zb etc for spellcasting.
' key swaps between items a and b (weapons), helpful for switching staves as caster or swords/bows for melees;
= i to adjust weapon letters to a/b.
That's all I can think of for efficiency
speed still comes from knowing the danger level well. And 7 hours for lvl20 sounds fast to me