refresh for slideshows should be multiplier, not set values

as discussed, refresh for slideshows should not be fixed (as the current dropdown provides preset intervals), but a multiplier.
multipliers could have a range ~ like 0.1 0.2 0.5 0.7 1 1 1.5 2 3 5 10 20 (values just as an example). by default multiplier is 1.
thus if a user had two slides with delays 10 and 20 and chooses to multiply by 0.5, slides get changed after 5 and 10 seconds. if user chooses multiplier 10, delays are changed to 100 and 200, always keeping relative difference.