Bad circuit layout is on the left, good layout is on the right
5V DC input gets regulated down to 3.3V using low drop out transistor
3.3V output feeds the supply voltage to the timer chip, as well as the quiet high test lines on the inverters
Test points were added to look at switching and instability noise on quiet lines, inverter/555 outputs, as well as the LDO 3V3 output and 5V rail.
Trace lengths are unnecessarily long
Decoupling capacitor C6 is far away from input on U2 pin 1
Lack of ground plane means some return paths are shared back to the bottom layer