I download SPSS version. The first 3 variables are id, submitdate, startlanguage.
The submit date is always 1-Jan-1980 for about 80% of the responses.
How do I get replies for all responses with a correct data/time?
A partial response doesn't have a submit date, a completed response does. Check that your survey is not anonymous and that datestamp is set to yes. For the recorded responses you can not fix this anymore.