This is incorrect.
Review Autoslew time settings. The GPS updates the clock as frequently as you wish not just slews, start and stops. I have Autoslew using the GPS to update every 3 minutes. This should be fine for most any exposure.
The fact that the PC clock is updated does not mean that Autoslew takes it into account between slews.
Anyway, a GPS update every 3 minutes is useless and may have more bad effects that good ones as most applications are not prepared for such clock changes and may react in a weird manner. Such clock updates are highly discouraged (when not completely forbidden) in real time systems, and a PC running Autoslew is one of them.
I don't know which benefits you expect from such a high frequency, and I am curious to see figures that show that this is helpful.
How to do set a GPS to make automatic updates during a session? I can't find this anywhere :-(((
Mike, I don't know as I don't use a GPS, I use NTP instead, and it is configured to update the clock once per day. But if you update your clock with the GPS at the beginning of your session, it is highly sufficient, as no updates during the session are necessary.