I always recommend a VERY short distance the 1st day.
See what your legs/body tell you on day 2 and adjust upwards if able.
When I got back into riding about 12? years ago, I didn't go that far, but I was mashing.
The next day my calves were so sore, I didn't get on the bike for over a week.

just add a little everyday and in a week you'll be going much longer and not be miserable.
Spin, don't mash. Don't be afraid to stay one gear lower than you think you can handle.