You can of course select a whole batch of photos in the timeline by the usual shift-clicking method, and thereby change the duration of them all as you would for just one.
I have been checking in David Pogue's otherwise excellent Missing Manual for iMovie 6, and that does not mention a defualt duration you can set prior to import. So I would suggest doing them in batches.
And then what are you going to do with them? iDVD has a 99 slide limitation. When I make slideshows using iMovie 6 and iDVD 7 I use this workflow:
If what you want is what I want, namely to be able to use high resolution photos (even 300 dpi tiff files), to pan and zoom individual photos, use a variety of transitions, to add and edit music or commentary, place text exactly where you want it, and to end up with a DVD that looks good on both your Mac and a TV - in other words end up with and end result that does not look like an old fashioned slide show from a projector - you may be interested in how I do it. You don't have to do it my way, but the following may be food for thought!
Firstly you need proper software to assemble the photos, decide on the duration of each, the transitions you want to use, and how to pan and zoom individual photos where required, and add proper titles. For this I use Photo to Movie. You can read about what it can do on their website:
(Other users here use the alternative FotoMagico: http://www.boinx.com/fotomagico/homevspro/ which you may prefer - I have no experience with it.)
Neither of these are freeware, but are worth the investment if you are going to do a lot of slide shows. Read about them in detail, then decide which one you feel is best suited to your needs.
Once you have timed and arranged and manipulated the photos to your liking in Photo to Movie, it exports the file to iMovie as a DV stream. You can add music in Photo to Movie, but I prefer doing this in iMovie where it is easier to edit. You can now further edit the slide show in iMovie just as you would a movie, including adding other video clips, then send it to iDVD 7, or Toast, for burning.
You will be pleasantly surprised at how professional the results can be!
To simply create a slide show in iDVD 7 onwards from images in iPhoto or stored in other places on your hard disk or a connected server, look here:
for this project, i do not need any panning, or Ken burns effect.... simply showing the pics very fast at 0:00:05 frame rate!
as an example I grabbed about 45 photos,( as a test) , and wanted to show these photo very rapidly, with a duration of 0:00:05. it would not allow 0:00:05. So I tried to do the batch change, with 0:00:10, and only the 1st photo would have 0:00:10, but the other 44 photos would have a default of 10 second each (0:10:00) ... (glitch in iM HD 6 I guess). I think when I used aything above 0:00:15, it worked.... but that what not the duration desired!
So I had to use command +i and command +V and paste the 0:00:05 individually to all f them...
Now my other problem is I attempted to "File-export to Qucktime", or "Share"... and nothing is happening.... i'm running OSX 10.8.2.... could that be the culprit?
I only want to export that to a quicktime file and will merge that into another quicktime moviefile with QT Pro..... but I cannot even export it.... what do I do?
I know nothing about the new iMovie 7 and newer! and I have to get this slide show on the road asap!
no so much animation, but showing a series of cars back to back in a rapid succession. it does work, I have done it in the past... but IMovie...seems not wanting to EXPORT anymore!
what is the problem with that?
now I went back to iPhoto 7, (cuz iphoto 9 does not do it either) and attempted to export, putting the time at 0:10 sec, but the "disolve" transition between the photo, lengthen the time of each slide back to about 3/4 of a sec..... not good.. do you know off hand, if the disolve can be turne off in iphoto, when exporting to quicktime?
correction: using iM6HD, i exported a QT self contained file (640x480) about 45 photos at 5 fps, and not .05 sec per photos... much faster succession of showing the photos! Iphoto 7 or 9, cannot export a QT file at that fast rate! (5fps)
Then for the remainder of the 644 photos, using iPhoto 7, (not 9), I exported at 0.5sec per photo, and with the "default" disolve in between each photo, I ended up with about 1 sec per photo, and with a final 24 minutes QT (640x480) self contained slide show. Then I merged the 2 files together using QT 7 PRO.