Check/compare modtime before deleting?

[Chris]

I need to keep two identical copies of files on my desktop and laptop,
so I want to use the -delete option.  But I don't want to delete files
that are created after last sync.  Is there a way to keep files with
modtime later than a file of a different name (a flag file created
before each sync) when using the -delete option?

Thanks and I appreciate any help.

-Chris