it is long enough to be an issue?
No, as evidenced by the huge prevalance of 555 chips. I presume the switching happens so fast that there's just practically no shoot through. It's worth noting that even your basic TTL not gate (with proper push-pull output) has the same """issue"""; the section you drew the rectangle around is a NOT gate after all. Also, the transistors involved are not massive power transistors; they're often rated for a short to ground for brief (by human standards) periods. Obviously having both transistors on at the same time is only half as bad as a short to ground, and it's for a period of time that is millions of times shorter. It's just not an issue. You may wish to try powering your 555 via a current sense resistor, and see the current pulses.
![](http://www.ibiblio.org/kuphaldt/electricCircuits/Digital/04073.png)
You may also wish to consider purchasing 555 CMOS chips, they are just faster, lower power, higher input impedance and better in every way.
![](https://rs20-static.firebaseapp.com/pano/cmos555.png)
Still "theoretically" capable of shoot-through, not that the current involved would be a problem, but I'm curious to see what you'd propose as a perfectly, theoretically totally shoot-through-immune push-pull output stage.
EDIT: Fixed broken image link.