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How much time it takes for the space capsules to descend from ISS back down to Earth?
Soyuz, Dragon, Crew Dragon, Cygnus, European ATV and Japanese HTV and any other such craft.
From the moment they undock from ISS to the moment they touch land (or splash into ocean water)
From the moment they undock from ISS to the moment they touch land (or splash into ocean water)
In the case of the Crew Dragon Demo-2 flight it was a little over 19 hours, but for most of that time the Endeavour wasn't descending, but just orbiting. From the initiation of the descent burn to splashdown was about 52 minutes.
Here's the planned return timeline (all times US Eastern time) from a NASA blog post the morning of reentry -- I assume they executed reasonably close to this plan, but I haven't confirmed any of the times:
Crew Dragon autonomously undocked from the International Space Station’s Harmony module at 7:35 p.m. Saturday.
Sunday:
1:51 p.m. – Crew Dragon performs claw separation. The claw is located on Crew Dragon’s trunk, connecting thermal control, power, and avionics system components located on the trunk to the capsule.
1:51 p.m. – Trunk separation
1:56 p.m. – Deorbit burn begins
2:08 p.m. – Deorbit burn complete
2:11 p.m. – Nosecone deploys
2:32 p.m. – Crew Dragon maneuvers to attitude for re-entry
2:44 p.m. – Drogue parachutes deploy at about 18,000 feet in altitude while Crew Dragon is moving approximately 350 miles per hour.
2:45 p.m. – Main parachutes deploy at about 6,000 feet in altitude while Crew Dragon is moving approximately 119 miles per hour.
2:48 p.m. – Splashdown
Unfortunately this timeline doesn't call out the crossing of the Kármán line but it should be closer to 2:32 than 2:44.
Of your list only Soyuz, Dragon, Crew Dragon safely make it to the surface of the earth. ATV, HTV, Cygnus, Progress all burn up during rentry.
For the first Crew Dragon mission, undocking from the station to landing is about 19 hours.
The perhaps more interesting question is more from deorbit burn to landing. Which Wikipedia has as just under an hour. (52 min).
The deorbit burn is about 11 minutes long. So start of or end of, for your request? Once they cross the Von Karman line to landing?
It is hard to give a single answer to these sorts of questions. Also different vehicles follow different profiles and often have multiple options in case of bad weather at the landing locations.
"From the moment they undock from ISS to the moment they touch land (or splash into ocean water)"
This time interval heavily depends on the position of the ISS (in the moment of undocking) in relation to the landing area.
If the ISS is in the optimal position, the capsule may initiate the reentry just after undocking.
If the ISS does not fly over the selected landing area during the next orbits, the capsule has to wait (doing some orbital maneuvers for the next hours) until a reentry would lead to the center of the landing area.
If they missed the optimal position for just some minutes, they have to wait up to 23 hours and 12 minutes for nearly a full turn of the Earth. The ISS needs about 93 minutes for one orbit, so 15 orbits take 23 hours and 15 minutes.
