Thank you all, it is only 4 commands that must not be disturbed by interrupt.
I use software reload and add TL0 to the reload (rewrite) value when entering the ISR, so there is no problem with response time.

Eric, could you please explain this:
"Btw it it very bad practice to set and reset IE bits as you do, Push IE, clear the bit and when you are done pop IE."

Fröhliche Ostern!

Carsten