In FCPX Preferences > Editing pane, there is an option for Still Images: Editing duration is X.xx Seconds[/Frames]. You can predefine the length of each image before applying them to the storyline (or, with the same option, upon importing the images).
FCPX will apply multiple clip selections in the order in which they are selected in the event browse (not easy to do for 1800 clips/photos though.) However, I think you can sort by name [or date created] and Select All then apply to the storyline in one move (I usually use E to apply all clips to the End of the storyline). Group by None, Arrange clips by Name Ascending before selecting all.
As Tom stated, you can reset the length each image is shown at any time by selecting all the images in the storyline and assigning their lengths with the viewer "clock" [Control-D, or double click on the clock and type the length in seconds.FRames - example: each image for 10 seconds 0 frames, type: '10.' (the period is necessary, the trailing zeros are not)] then type Return or Enter.
If you have Motion, you can open a folder of sequentially numbered images as an "image sequence" and render out a movie file (you can also adjust the "timing" before export). You can also do the same with Quicktime 7 Pro (File > Open Image Sequence plus you set a frame rate for the sequence).
If you find you have problems with timestamp names being used for image sequences, you can build a simple Automator application for (Actions) Files and Folders to 1) Get Folder Contents; 2) Sort Finder Items (by name or date created descending order) in a folder passed to (dropped on) the app, then 3) Rename Finder Items by "Make Sequential" (chosen from the dropdown menu); Add Number to new name (type a "root" name like IMG or Seq, etc.); Place number after name; Start numbers at 1; separated by dash or underscore; check Make all numbers 4 digits long. You'll see an example at the bottom of the Rename action as rootName-0001.xxx. You can opt to copy all the original files first, but if done correctly, it's not necessary and you end up with exactly what you want without having to manually go through every file and rename it. Save to a convenient location and drop your images folder on the desktop icon. (Test it on a folder with just a few image duplicates first.)
