ULPNode Low Power - How to calculate reserve capacitor capacity?

[mj]

Hello,
after building my first version od DC/DC booster as described here I have testes few capacitors 33uF, 45uF and at last 1000uF (electrolytic, low ESR) - it needs about 60ms to get fully charged.
Test circuit with white LED 20mA lightup + fading. Time I got between recharging is about 1m30s.

My question is: Is there any equation to calculate optimal capacity/charge time, to achieve best power efficiency?

Correct me if I'm wrong in my approach to find size of reserve capacitor with charge time equal to time I need to take all measurements, send data with RF module and receive ACK and go to sleep.
So not to draw power from booster only to run uC (atmega328p) while capacitor is already charged?

Right now I have made self running power circuit ( BATT -> MCP1640 -> NCP302 + IRF7410PbF) where time is regulated by capacitor attached to pin 5 (CD) of ncp302, so system is autonomous.

In context of regulating time before measurements I think it's a must to do it on uC site, because I don't see reason to change capacitors for every time change.

So:

• wake up uC
• increase counter
• go to sleep
• every X times wake up all devices take measurement
• reset counter
• go to sleep
  is the best and only approach.

This X should be given to node form Gateway during first start or config.

Any comment about capacity and wake approach?