I see 3 Options for you:-
OPTION I:
If you now have the VASST Event Tool,
1] Selection Tab : Select All Events > APPLY
2] Adjustment Tab : Adjust Selected Event Length to 00:00:10.00 > APPLY
3] Transition Tab : Change the “Length” to ZERO > APPLY
All Stills will now be at 10 seconds.
OPTION II
If you DON’T have the VASST Event Tool and DON’T yet have your Stills on the Timeline,
1] Main Toolbar > Options > Preference > Editing Tab
2] And adjust “New Still image length ” to 10:-

Drag Stills to Timeline, job done!
OPTION III
If you ALREADY have Stills on timeline then create a Group of ALL the Stills and use the Ctrl+Drag method to stretch stills to the required length.
Cheers
Grazie
Video Content Creator and Potter
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