6v6gt:
As an alternative to trying different hardware, why not try to optimize the existing pro-mini. 4mA is far too much in sleep mode. You should get down to a micro amp or so. Some pro-minis have a trace you can cut to disconnect the power led and the regulator (assuming you are powering it at less than 5.5 volts). Also look here for ideas: Gammon Forum : Electronics : Microprocessors : Power saving techniques for microprocessors
You are right.
I thought that what was eating power was the TM1637 based led display, I turn off the display before going to sleep with
display.setBrightness(0, false);
display.setSegments(alloff);
But to make sure, I just yanked it from the breadboard during and nothing changed, still about 4 mA.
I still can remove the power led and the LDO.
Power is being supplied by 2 AA 2450 mA/h Ni-MH via a boost converter to 5.0V so lowering the voltage is not possible (this boost converter have fixed output).
I tried to divide the clock but it affects the milliseconds ticking, I'm not using delay() only reading the time with millis() I don't know how to solve this.
And this board with the Attiny167 is a bit smaller than the pro mini, this is a good thing,