You can use the Offset Dates option in the Manage Dates tool to change all of the start and end dates in your course at once. You can find instructions for using the Manage Dates tool in the Manage Dates D2L guide.
As the Manage Dates guide outlines, if you enter whole numbers, the dates will change. But you can also change time using this tool – you’ll need to enter a decimal point. Here’s how you calculate it:
number of minutes you’re changing the time / 1440 [number of minutes in a day]
30 minutes / 1440 = 0.0208333333
Usually you’ll end up with a long figure, just like the example above. This isn’t a problem, however, since D2L will let you enter long figures in the Manage Dates tool, even though it will only accept up to two figures after a decimal in other parts of the system.