My Bolognese sauce usually contains some combination of salt, pepper, basil, oregano and thyme. It is easier to taste if I add them towards the end, but is the taste affected by when I add the herbs to the sauce?
Salt is added at the beginning, because it takes long time to dissolve. Also, it's maybe less important for bolognese, but you want your veggies to get infused with salty water, the taste is different from bland vegetables swimming in water salted late. Last but not least, salt's chemical properties are important for the cooking of some dishes.
The stuff which depends on volatile aroma molecules (practically all fresh herbs) is added at the end, after the sauce (or stew) is removed from the heat, because lots of the compounds are destroyed by heat, and while the flavour is still discernible, it is diminished.
On the other hand, if you are using dried herbs, their most fragile molecules have long since disappeared in the air. The flavours which remain in the dried leaves are sturdier and not easily loosened from the plant matter. So by adding dried herbs early enough to allow for some simmering, you can leach more of these out of the leaf (you are practically steeping it in the sauce). But if you cook them for too long, even these molecules can get damaged. Plus, there were some herbs which release unpleasantly bitter alkaloids after too long a steeping (I don't remember if your three are among those, but I would suspect the basil may be, as it is prone to producing off-tastes). So add them ~5 minutes before turning the heat off.
Spices are a bit of a boundary case. Although dried spices don't taste the same as fresh ones, grinding them still releases volatile molecules. So I tend to add them at the end, like fresh herbs, and I'll advise you to do so too (using peppercorns in a grinder). If I use spices which were bought pre-powdered, I throw them in earlier or together with the dried herbs.