A delay is normal in most MB trannies going into reverse. Some models it can be worse. Your trannie does have an external reverse band adjustment though, that should only be adjusted by one with experience.
If it is too tight it can cause the band to self energize and lock up the beast in two gears. I have had it happen to me twice (at about 10mph), scarry!
Bosch Master, ASE Master, L1
33 years MB technician