When creating a new sequence, after you click animation the sequence setting window opens up. If you already have a sequence created, go to Settings/Sequence Settings.
On that window, click the Timing Tab. At the bottom of that, click "New." In the window that opens, change the Select New Timing Interval to Metronome and click OK. Enter in the timing that you want to use in milliseconds, so for 20 second spacing, enter 20000 and hit ok. You'll now have a new timing track with the spacing you chose there for all the marks.