Here is a possible client side solution. Create a database activity in the designated course site and apply the attached preset. Add a new entry and enter to the quizzes field a list of the quizzes as a bulleted list in the following way:
The first value in each item is the quiz id.
The next five values are the quiz open date and time: day (1-31), month (1-12), year (1970-2020), hour (0-23), minute (0-55 in steps of 5).
The last five values are the quiz close date and time.
The data must be clean so if you create the list in excel you need to copy it first to plain text and only then into the entry where you can convert it to a bulleted list.
Save the entry and go to the single view to run the updating script. The script assumes correct data and does not perform any validation. It uses a hidden iframe in which it opens each quiz for editing set the date values and submit. 200 quizzes may take some time to update but the script doesn't mind that.
Tested on 1.9.4+ but should work on any 1.9.x.
Hope this works for you.