The average time between undocking from the ISS and landing on the planet takes roughly six hours to 30 hours depending on the position of the station with respect to the splashdown site in this case. The two astronauts have been part of several science experiments onboard the ISS, including two extravehicular spacewalks conducted by Bob Behnken to repair the station for continuous usage.
Separation confirmed. Dragon performing 4 departure burns to move away from the @Space_Station pic.twitter.com/ea14fozdO8
— SpaceX (@SpaceX) August 1, 2020
According to Nasa, "several hours later, one departure phasing burn, lasting about six minutes, will put the Crew Dragon on the proper orbital path to line it up with the splashdown zone. Shortly before the final deorbit burn, Crew Dragon will separate from its trunk, which will burn up in the Earth’s atmosphere. The spacecraft then executes the deorbit burn, which commits it to return and places it on an orbit with the proper trajectory for splashdown."
Once the spacecraft enters the Earth's atmosphere, two sets of parachutes will deploy at an altitude of 18,000 ft slowing it down to 350 miles per hour. Further along, four main parachutes will deploy at about 6,000 feet bringing it down to approximately 119 miles per hour as it splashes into the final site.