The gallery batch uploader processes images in the order they are uploaded to the server.  Be aware that many ftp programs use multi-threading to upload, so just because image_1 is before image_2 when you ftp them to your server, they don’t necessarily arrive in the same order.  To ensure that they do, turn off multi-threading in your ftp program.  The images will then arrive in the order you upload them, they will be processed by the gallery batch entry in the order they arrived, and they will then sort by date in the order you expect.

See forum discussion for details.