I don't have much faith in server synchronization date & time stamps. Too many things can go wrong.
I prefer the following method. In Files Panel, right click on your local site folder. Select > Recently Modified.

Choose a time interval (4 days) or the date between today and your last remote site update.

DW will highlight all recently modified files including images that were modified outside DW.
Click the UP arrow to upload files.
Use Cloaking on files or folders you don't plan to update again. You can always uncloak them later if needed.

Nancy