I don't think they have plans to do the fight the same month or even the same week with Casimero fight against Butler.
There's actually nothing wrong if the fight will be held the same month but should not be on the same week.
But my concern is, how's the preparation time? There could be an advanced prompt that those 2 boxers received to prepare early which is not disclosed to the public because their match is likely to happen.
I read the article and it's clear that Arum pointed out that the match is in April, not a signing. But I agree, it seems a rush. They can do it the month later which is in May but if there's no problem between Inoue and Donaire, then all set up next month.
Yes, that's the point, it's a rush, boxers needed at least a good 8 weeks to train and then we have the promotion.
So we will see, maybe they are really started this training already and just didn't divulge it to the public. We all know that Arum is a master planner so this could be part of his grand plan about this fight. Create hype and portray that they don't have enough time to prepare for the fight.