@Sweebee Got it working last night (I hope!), I haven't measured the power consumption yet.

It doesn't have the resolution of ms. To save battery the attiny85 will sleep for 8 seconds, then wake up and go to sleep again. So if you call gw.deep_sleep(7), it will sleep fox 7x8=56 seconds. It is possible to get a more precise timer by calculating the best combination of sleep timers. For example if you want to sleep a minute, sleep 7x8s=56s and then an additional 1x4s=4, total 60s.

It needs some cleaning up and correct naming/commenting/testing e.t.c.

void MySensor::deep_sleep(int time) {
	// Sleep alternatives:
	// 0=16ms, 1=32ms,2=64ms,3=128ms,4=250ms,5=500ms, 6=1 sec,7=2 sec, 8=4 sec, 9= 8sec
	int ii = 9;	// sleep 8 seconds at a time.
	byte bb;
	int ww;
	if (ii > 9 ) ii=9;
	bb=ii & 7;
	if (ii > 7) bb|= (1<<5);
	bb|= (1<<WDCE);
	ww=bb;

	MCUSR &= ~(1<<WDRF);
	// start timed sequence
	WDTCR |= (1<<WDCE) | (1<<WDE);
	// set new watchdog timeout value
	WDTCR = bb;
	WDTCR |= _BV(WDIE);
  
	// Count some sheeps.
	for(int i=0;i<time;i++) {
		RF24::powerDown();	
		cbi(ADCSRA,ADEN);                    // switch Analog to Digitalconverter OFF
		set_sleep_mode(SLEEP_MODE_PWR_DOWN); // sleep mode is set here
		sleep_enable();
		sleep_mode();                        // System actually sleeps here
		sleep_disable();                     // System continues execution here when watchdog timed out   
		sbi(ADCSRA,ADEN);                    // switch Analog to Digitalconverter ON
	}
}

Awsome work Oitzu and Sweebee!

Just tried it out and it works perfect

Have you succeeded with getting the sleep/timer working? I've tried but discovered that my skills aren't good enough.