I know that just click on the edge of the photo and drag it to change its duration, but by chance, there is an information box (like "time"), that I just need to type in the number of seconds and this does it?
Each photo must have a different duration.
Look at the keyboard short-cuts, which can be found under the Help menu or the owner's manual and check out event edge trimming. You press "[" to enter left edge, "]" for right edge. Then the edge of the event will be highlighted red that you're editing. Press NUM Keypad 1 or 3 to trim the photo by 1frame, Press NUM keypad 4 or 6 to trim by " 1 Pixel". Pixel is a zoom dependent edit amount, where the further you are zoomed in, the finer the edit amount becomes.
There are other key definitions in the keyboard short-cuts aside from the ones I mentioned for different key assignments for the same function. For example, I believe NUM keypad 7/9 also double as the [/] trim edit mode brackets. Definitely worth exploring the KB short-cuts to see what you can do. I believe there are also some trimming mouse modifier keys, such as pressing CTRL,SHIFT, or ALT while dragging on the edge of an event with a mouse that will give you finer edit amounts, if you prefer that method. Personally, I can't stand editing events with a mouse, but do so only when I forgot a particular KB short-cut.
Not directly, but here is an indirect way. Double-click on the image on the timeline and this selects the whole image. Then go down to the right of the screen where it shows the IN, OUT, and DURATION of the selection. Double-click on the duration and type the duration that you want. Then it is easy to drag the edge of the image to snap to the end of the selection. Not a quick method but you can get it exact without guessing while dragging the edge.
In a video project, the duration of a still image event is determined by frames, not time. For instance, in a true 30p project, one frame is .333_ ms, and that is the smallest precision possible. To prevent weirdness, make sure Quantize to Frames and Snapping are enabled before adding media to the timeline. Time and Frames is the easiest time format to use, at least for me.
Or, you can use this very simple script. Just select the photos and set your length. There is also an option to close the gaps if created. Here's a screenshot.
And here's the link where you download for free. https://tools4vegas.com/set-event-length/
If you have Vegasaur, there is also a way to do this:
Editing - Quick properties - Events - Extend Event
There are many roads to Rome, but they are sometimes very hidden 😃
In VP 17 you can enter the length directly at the event.