We have a four hour layover in Vienna later this month on a Saturday morning from 8;45 am to 12;50 pm. This is before we fly on to Dubrovnik. both flights are on Austrian Airways so hoping bags are checked all the way through. Is that enough time to leave airport and see a bit of the city? too risky?

In the best case, you will arrive at Wien Hbf (city center) at 9.38 and will have to go back from there at 11.15.
In these 90 minutes, you can do almost nothing.

>>Is that enough time to leave airport and see a bit of the city?<<

No

>> too risky?<<

Yes

>>In the best case, you will arrive at Wien Hbf (city center) at 9.38<<

That would be pretty optimistic, since you might still be in Immigration at 9:38.

This is really a booking time rather than an after the fact question.
As mentioned above, this is difficult to do at WIE.
- Unlike AMS or FRA, the train station is somewhat of a trek from the airival.
- The trains don't run as frequently from WIE, and the trip to downton takes longer, and you are NOT yet in the center of the city.
- You are arrving at the peak time at WIE. If you are arriving from a non-Schengen country, many mega jets from the US and Canada are arriving at the same time further delaying going through the passport control.
When I see a layover like this offered, I look for a shorter layover itinerary when I don't care to linger at the layover city. If the layover city has much to offer, I tinker with the itinerary, without adding too much to the price, to extend the layover during the usable time. A 4 hour interval during the day is more usable than a 10 hour interval between 10pm and 8am unless you are doing something like in the movie "Before Sunrise."

Gotta go with, "No." We live in Vienna and agree with everything posted. You do not have enough time to leave the airport to see anything but the Autobahn as you circle back for your departure.