Does Google Maps take into account hills/inclines for route times?

No. Google Maps works a different way.

Google Maps learns travel times by monitoring the pace of other riders.

The Google Maps app "constantly" sends data about your location back to the Google servers. It knows you're on a bike, not driving, because you requested a bike route, and because your travel time is not an outlier from other people doing the same.

And that's also true for driving; though of course Google gets more data for drivers, so driving data is fresher.

Yes, really. Google "spies on you" and observes your movement, nominally for this exact purpose (but they won't refuse a subpoena in most cases). And yes, you agreed to be a lodestar for others, at some point when you clicked "agree" on a term-of-service while interacting with a Google product. You can deny Maps access to your location, but then of course, it wouldn't work at all.

This tracking is fairly continuous, even when the screen is off, which means Google knows when you stop for a break, and excludes that time from the data.

This provides a very authentic transit time without having to do deep calculation on the effect of grades, tight curves, congestion and road condition on ideal travel times. For instance if a flat, straight rail-trail is heavily overgrown with brush to where you must slow to maneuver around a thicket of overhanging branches, it captures that reality.

At least for bikes it does (assuming the topographical information mentioned in the comment is available).

I just checked with two cycling routes near my home, both 4,2km long according to Google, one almost flat, the other with a climb towards the end (obviously going downhill the other direction). Result:

1. 4,2km almost flat but slightly downhill: 14min
2. 4,2km almost flat but slightly uphill: 15min
3. 4,2km mostly flat (3km), but a climb towards the end (1,2km): 17min
4. 4,2km mostly flat (3km) and going downhill at the beginning (1,2km): 12min

If these numbers are of any relevance certainly depends on your bike and your fitness level (and probably some other factors, too). I hate riding uphill and my bike isn't made for it, so whenever I had to "cycle" up the hill at the end of no. 3 I would get off my bike and push it, certainly losing more than two minutes compared to a flat route. The same goes for downhill, I doubt I was ever letting my bike run so fast I would acutally gain two minutes...

Short answer: Yes absolutely google maps is aware of elevation changes.

Longer answer: ...but its fairly far from correct.

Example - There's a well-travelled local climb of 2.5 km and 140 metres elevation change. Its an average of 5% but is 10% at the top with a flat bit at the bottom.

Google maps predicts 13 minutes to descend and 18 minutes to climb. That's roughly 40% longer to climb than to descend, which is utterly wrong.

I personally descended in 3:25 and best climb in 10:30, for a 300% increase in climb time vs descent time.

The 20 top riders have descended in under 2:30 and have climbed it in under 6:00 minutes for a 240% difference.

So google maps should be predicting a climb in 39 minutes for a descent of 13 minutes
or a climb of 18 minutes and a descent in 7:30.

tl:dr yes google maps is aware of elevation changes and does try to take that into account, but doesn't fully account for the increased work required to climb a gradient.

Further info:

Walking is predicted to be 40 minutes to climb and 34 to descend.

Driving is predicted to be 3 minutes either way.

Link to route on Google Maps

Strava segment for uphill

Strava segment for downhill

Site is in New Zealand, near Christchurch. I'm roughly in the middle of times for riders on those segments, slower uphill and faster downhill (mass advantage there!)