Whenever I start a league or ML, I have to set the time of day as 'Night' or 'Day'. However it then remains either one of those for the whole season on every match. Is there a way to make this random as I don't think there is an option to change it before every match, only when setting up a new League/ML.

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it is random in ML, I play day and night

Your right it has the option for both day and night but if you scroll one more time you should see "Random".:D

I would like to pick my pitch...for Arsenal pitch is always greyish :f***:

Yep, random games here too, though I always seem to only play at night when playing at Lens or Auxerre, and it usually rains when I play at Fulham.