Sometimes, push messages are shown in the reports outside of the schedule of Push Messages. For example, push was scheduled for 09/25/2020, however, reports push messages instances on 10/20/2020.
The Users that Opened Push report shows hits for - when the user opened the push notification on their phone, based on their device settings. Most of the users will open the notification immediately (assuming they open it at all), but some users will delay opening the notification. The latter could be days later and then the hits would be sent to them. The data on this report is in-line with the assumption that the majority of users open the message on the day it is sent with a small percentage opening it at a later date.