I'm no longer getting collection items from the Magic Tower event, even though the timer is still there!
Magic Tower events generally start on Thursdays at 12:01am CET/CEST, and end at midnight Monday going on Tuesday the following week.
At that time, the collection timer changes to show the time left to pick up the prizes you've earned, or buy missing collection items. This period ends on Wednesday at 11:59pm CET/CEST.