You started at 10:20 pm on April 18th and finished at 12:06 am on April 19th. This means that the time elapsed is between two different days. To calculate the amount of time spent doing that thing, we need to subtract the start time from the end time.
First, let's convert the start time to 24-hour format, which is 22:20. Then, we can subtract 22:20 from 00:06 (12:06 am).
00:06
- 22:20
____
01:46
Therefore, you spent 1 hour and 46 minutes doing that thing.