After 23:55 the time selections go to 5 minutes, 10 minutes and so on until 01:00 then everything seems ok.

To recreate:
Start MediaPortal
My TV
Scheduled
New
Select TV Channel (1)
Select Recording Type (Record Once)
Date (today)

On the next screen, times are listed as XX minutes for times earlier than 0100AM - they should be 00:XX.