This is my solution. Maybe not correct, but...accuracy is VERY good !
I read the sensors (each) twice in a minute ; i add the timex variable, for increase 'the duration' of seconds when PIC read sensors, in step of 200 us. From various tests (many guys from one romanian electronics forum) , with 800 us the clock run correct !
Every advice it's wellcome !
Code:
	if seconds=20 or seconds=50 then              'read first DS18B20
		intcon.7=0
		gosub temp_1
			for i=1 to timpx
                  pauseus 200
			next i
		intcon.7=1
	endif
	if seconds=25 or seconds=55 then              'read second DS18B20
		intcon.7=0
		gosub temp_2
			for i=1 to timpx
			pauseus 200
			next i
		intcon.7=1
	endif