Try using 5.0.7 beta.
This change may help you:
https://winscp.net/tracker/568
See also:
https://winscp.net/eng/docs/timestamp

I have Excel 2003 writing a text file on the hard drive every second.
Is there any way winscp can keep the remote directory up to date with this file that quickly?
It seems to only upload once per minute.
I'm using 4.37, using the following code:

option batch abort
option confirm off
open user:pass@mysite.com
cd /<my remote folder>/
keepuptodate <my local folder> <my remote folder>
close
exit