You can change the setting  for every log windows you have without effect on the preference setting, used when you open a new window.
To change the setting for  a already opened Log Window:
Click in the window to bring them on the front if in the background , and from the menu 'Update' select 'Update Every...'
Here is possible to insert the interval time between a successive log update.
Log watcher at every interval time will display a fresh version of the log.
To change the size of the last portion of the file to read  select 'Load Last Kb...' from the 'Update' menu

Selecting a small dimension will make the upgrade process faster.
The smaller the interval times are, the more it's better to have a small interval time update not to  hog your Mac.
Thanks to this feature the upgrade process of the window will take a fraction of second.

If you need to wrap the log file choose 'Wrap' from the 'Update' menu to insert at which column insert an additional return.