Hi there,

There is not a specific "yes" or "no" answer in this case. Technically it is possible but you'll have quite some implications you have to mind. Currently the last Odoo version is 11.0, while the Odoo SaaS environment is running on SaaS-11.3. This means that the Odoo that is hosted on the SaaS platform is ahead of the Odoo version that non-SaaS people are using. This means there is a difference in the models and views which would need to be handled.

The easiest moment to migrate from the SaaS to an on site Odoo instance is when a new version is just released (11.0, 12.0, 13.0) as the database models for the on premise Odoo's and the SaaS Odoo's are almost exactly in tune then. If you really want to get away from the SaaS as fast as possible you could install an Odoo SaaS-11.3 on site. The downside here is that you will have no migration scripts by hand and you're kind of locking yourself into version 11.3 at that point. This might make things more complex for the future.

In general it is usually best to wait to a major version release and to plan the migration so that you don't miss the best moment.

Regards,
Yenthe