As Capt Fathom mentioned I've seen flight plans that climb, cruise for a couple of minutes (<10), and then descend. I've had some that literally touch the climb altitude and immediately start a descend. Looking at a flight today - 18 minutes of climb, 11 minutes cruise @ FL300, then descent. A flight on a longer leg (2.5 hrs) also had 18 minutes of climb. A longer flight (8+50) had 24 minutes of climb. A 13+26 hr flight had a climb of 19 minutes. So the typical climb time is 20-25 minutes.
On shorter flights, in high density areas like NW Europe, NE U.S., you'll be assigned altitudes based on ATC airspace requirements and not aircraft performance reasons.
As Checkerboard mentioned airliners usual don't go to their maximum altitude. OPT ALT is 2000-4000' under MAX ALT depending upon aircraft type. Ignoring winds the flight plan brackets OPT ALT, slightly higher until slightly lower, than climb to a new cruise altitude slightly higher than OPT ALT and as fuel burns off waiting until OPT ALT is below your cruise altitude and you climb again. Typical plan is to climb to 1000' above OPT ALT and repeat once you're 1000-2000' BELOW OPT ALT after fuel burns off. Strong winds change the calculation as the impact on GS is greater than the inefficiency of not flying near OPT ALT. With very strong headwinds you might be 10,000' below OPT ALT. That's unusual but being 4-6000' below OPT ALT against headwinds isn't that unusual. With strong tailwinds you do see cruise altitudes right at MAX ALT but the performance margins are smaller so it there's some consideration that goes into accepting that altitude, especially if you're going to be in a non-radar environment and changing altitudes might not be an option.
Last edited by misd-agin; 8th Nov 2020 at 03:04.
Reason: changed 1000-2000' above OPT ALT to "below OPT ALT."