At last program begins to work when I place
PIR1.0=0 ' Reset TM1 interrupt flag
into Tickcount ISR giving overflow times of 65.8/132/263.6 and 524.7 msec according with Prescaler.
WDT_ON or WDT_OFF apparently does not change results

Tickcount:
ShTemps=ShTemps+1
LCDOUT $fe,$C0,#ShTemps ' display
resume
enable

Thank you Skimask for your help
-Francesc