When I create a site event in Totara 1.1.11.1 I get an error saying that the event start date can't be before the course start date.

This is because $form->timestart isn't created by the time the validation function runs.  I have fixed this by creating $form->timestart in the validation function, but I don't see how this could have ever allowed site-wide events to be created.

Piece of related trivia - the non-existance of $form->timestart  meant that the comparison being done was (NULL < "0") which is true.  If instead it was (NULL < 0) then it would correctly come out as false.

A patch for this is attached, though it may make sense to add this field before the validation function is called rather than temporarily creating it in the validation function and then again once validation has passed.