Hi Linda B,
I'm a relative newbie myself but I have learnt a lot while I've been fiddling around with PD7, mainly thanks to this forum and the tutorial videos.
I haven't found any indication that the feature you're describing is available in PD7, but I can tell you what I do to adjust the timing.
This is possibly not THE answer, but it is an idea I have used manipulate the timing of a slide show, imprecise though it is.
1. Import the images
2. Make the slide show according to your own preferences/needs... make it look the way you want it to
3. Click Produce to render it in a video format.
4. When it's in the timeline, right click on it > Edit > Speed
5. Adjust the speed to suit your needs.
6. Produce again to save the file.
Example:
Started with a slide show with less than 20 images (motion template). Produced it to a clip lasting 1:02:00 (1 minute 2 seconds)
Adjusting the speed gave me these results...
Original Clip Modifier Final Time
1:02:00 1.1 0:56:11
1.2 0:51:20
1.3 0:47:21
1.4 0:44:09
1.5 0:41:10 etc etc etc
and slowing it down...
1:02:00 0.95 1:05:09
0.90 1:08:27
0.85 1:12:29
0.80 1:17:16
0.75 1:22:21
0.70 1:28:18 etc etc etc
For my purposes, this works... but there's possibly a more accurate way of doing it.
Tread gently and you'll hear the daisies grow...