No it isn't. Why wait 'til an arbitary time? A manager still has to manage in the Summer. He presides over transfers, oversees fitness, plans for the following season etc. A new, competent manager could come in next week, assess the current players and plan for next season in a position of authority.
This season is a lost cause. Sacking Martinez won't relegate us, but it will give the next guy some time to work his own vision in preparation for next season.
Sacking Martinez would risk de-stabilising this squad which is full of players he has brought in... and I don't agree with sacking your manager half way through the campaign.
This time last week everything was rosy. Sick of fickle fans.
We got done today and it happened. We have to move on from it and start again.