I have had instances where we have had scheduled webinar times randomly change from 10am - 12pm to 10am - 11am, why would this happen? it has happened in the past, we have been through and triple checked them and today it has happened again on a webinar we were running this morning.
@Innovation1 I've not been able to find instances of a Webinar duration changing randomly.
Your best bet would be to contact Customer Support with the affected Web ID so we can investigate what may be happening with these particular webinars.