How long does it take for one to get settled on a new saddle? I recently switched from a Selle Royal Seta T1 saddle to a Shimano Pro Falcon Anatomic saddle with a cut-out. It's lighter, wider (152mm), and has lesser padding than my previous saddle. The first ride I did with it was 100-km ride, in which I was on the saddle for around four hours. Apart from pain around the sit bones area, it was comfortable. To date, I've ridden 163km in total on the saddle, so three times in total, but every time I have ridden it, my sit bones have hurt. 

I am wondering in general how long does it take for a saddle to break in, so to speak. Or, is this a case where this particular saddle isn't right for me? 

I'm a heavy rider at 88kg, and I ride mostly in the saddle. I chose a 152-mm wide saddle because it more closely matches my sit bones measurement, which came around 15cm. 

Thank you.
A 100 km ride is too much to do on a new saddle -- I'd start with 30 minutes rides, hour tops; not too hard. You also need breaks between rides -- riding 100 km then 30 km every day after will probably start you sore and keep you sore.

The saddle won't really change appreciably (break in) as you use it; break in is really for leather saddles which can break in like baseball gloves over time (and even then, theres only so much that can happen -- it either will fit or won't). Either you'll get used to it after a few rides or not. Many better bike shops have a return period for saddles that is long enough that you can probably get in 5-10 rides to get an idea if its comfy or not. 

It's a highly personal decision, with body type, bike type and clothing choices coming into play.

Also, make sure the saddle is properly adjusted -- this means adjusting angle, fore/aft position, height, etc; switching saddles isn't as simple as just putting the new saddle in exactly the same position as the old one. You may even end up adjusting the handle bars a bit; saddles can feel too narrow if you have to sit too far forward.