Sorry to hear that you’ve run into this issue! Saving will be almost instantaneous and there should be no delay. What you can try, is save again (or save another photo from Ribbet) and take a look at the file path in the File Save dialog that appears right after you click Save. You will most likely see your saved collage in the dialog and hopefully be able to locate it with that information.
Note that on Safari on Mac OS, all files are saved to the Downloads folder.
Regards – The Ribbet Team