Timeshift should not behave different between you sitting in front of the machine or not, normally...

May as well be you have some energy saving related trouble.
Check sleep mode settings, as possibly some component does not wake up soon enough, before ProgDVB scheduler starts a recording.
Either don't allow your tuner to fall asleep, or modify tasks to allow more time for wakeup before start record.

thanks a lot
i hope next information help you to get me solve

My power plan is :

turn off the display : 20 MINUTES
PUT THE COMPUTER TO SLEEP : NEVER

OTHER ADVANCED OPTION ARE :

REQUIRE A PASSWORD ON WAKEUP :YES
TURN OFF HARD DISK AFTER :NEVER
DESKTOP BACKGROUND SETTINGS : AVAILABLE
Wireless Adapter Settings : Maximum performance
SLEEP
SLEEP AFTER : NEVER
ALLOW HYBRID SLEEP : ON
HIBERNATE AFTER : NEVER
ALLOW WAKE TIMERS : ENABLE
USB SETTING : ENABLE

PCI Express : MODERATE POWER SAVINGS

PROCESSOR POWER MANGEMENT
MINIMUM PROCESSOR STATE : 5%
SYSTEM COOLING POLICY : active
MAXIMUM PROCESSOR STATE : 100%
display : 20 minutes
Multimedia settings
when sharing media : Prevent idling to sleep
when playing video : balanced


regards:D

Requesting a password after the display fell asleep may perhaps lead to trouble.

To find out more, disable that display turnoff timer, set to always on. You can still turn off the screen manually, to save the power for it.

Or disable the password protection for wakeup.

Yet another way to go may be, to turn off the video decoding before letting the machine do a timer job.