The Classic view allows for entering exact time and date info a custom "Date Time Picker" field, However, the New Issue view has removed the granular time entry option and replaced it with a 30-minute increment picker list option, and can cause up to 15-minute discrepancies in time values where more precision is required.
i.e. the desired time entry is any value from 1:01 to 1:29, you are limited to 1:00 or 1:30 as the only available options
Add the ability to manually enter the time as needed for the custom time field
The following Workaround is only available until Mar 31, 2021 noting:
Disable the New issue view by navigating to your user icon in the upper right of the screen, and selecting "Personal settings" then scroll down to the "Atlassian Labs" section and deselect the green selector slider for the new issue view:
once disabled date and time fields can be modified as needed