Powering up DAGU 4 channel motor controller and logic at same time - Problem?

I have wired up my Dagu motor controller to the same switch that gives power to the logic (ie Arduino board) - they are on different circuits though...

The DAGU instructions say to power up the logic first:

"The motor power supply should not be connected without first connecting the +5V for logic."

Is this (ie powering them both at the same time, or the logic slightly delayed - it goes via the Arduino board regulator) going to be a problem?   Why does the logic need to be powered first?

Also, if it *is* going to be a problem is there a simple fix so I can keep one on off switch?

Thanks -I have wired a 9v

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What would a 7.4 lipo

What would a 7.4 lipo battery do to the controller?