I often find that a brown chicken stock when reduced is quite bitter, since you have to reduce the stock down so much in order to take it to sauce consistency.
If I want to add roasted flavors to my sauce, I will just use meat/trim/bones from whatever I'm making a sauce for and fortify that by roasting. So, for example, if I want to make a lamb sauce I'll take all the scraps from butchering lamb (and bones if I have them) and roast those, deglaze with wine, etc, then add the stock and aromatics and reduce to glaze.
I don't make veal stock very often since it is pretty cost prohibitive. I almost always make a white veal stock as well, but I add tomato which gives it a brown color when it reduces.
I'd say anything more than 6 hours for chicken stock is overkill. I do 8 to 10 for veal, then make a remy obvi (gotta get all your money out of those bones lol).
Earlier in my career I worked in a place where we did a veal stock in a steam kettle for like 48 hours. I dunno, but the stock was always really bitter, flabby and not pleasant. Sauces were thin. Something wasn't right. Dunno if cooking too long was an issue, or what.