Do they mean "An annoying prank that maybe okay in April's fool, but not right now."
Or do they mean "A prank that's more fitting to be done in April's fool, but it's welcomed nonetheless."
Do they mean "An annoying prank that maybe okay in April's fool, but not right now."
Or do they mean "A prank that's more fitting to be done in April's fool, but it's welcomed nonetheless."
"Off season April's fool joke" is not a commonly used expression; therefore, you need to deduce whether the joke was welcome or not from the context. I believe the intent was to indicate that the joke was the kind of joke that would be done on the 1st of April (which does not necessarily mean even then that it would be welcome).
Off-season is an expression which just refers to a particular time of year when a particular activity is less commonly (or never) performed and the place hosting the activity is not busy. Typically, it refers to holidays, sporting or leisure activities. For example, February would be "off season" at a European seaside resort.
An "off-season" event is simply one that is performed outside of its usual season. For example, a Christmas party in May would be considered "off-season". It normally refers to sports or popular holidays, but in theory could apply to anything with a season.
April Fool's Day (April 1st) is traditionally a day for playing pranks. An off-season April Fool's prank (or joke), therefore, is one that was not performed on April 1st.