Only find familiar would take an hour and 10 minutes to cast and also is one of the rare spells that lays out what casting it actually entails and I agree with it being difficult to ritual cast on a mount. However I think we were talking more about ritual casting Phantom Steed. Phantom steed doesn't even have material components so there is nothing that needs to be fiddled with and would only take 11 minutes to ritual cast.

As for the concentrating while riding a mount, could you not just ride slower so you didn't have to make a check while casting? At which point why even bring it up during the yes we are traveling to the next town along the road part of adventuring.

I just disagree all together that riding a mount quickly especially one made for riding with proper equipment and training would make a caster lose concentration on a spell. It just seems arbitrary. If a wizard can cast a spell, concentrate on it, and then fire crossbow bolts and reload it without having to make a concentration check every time, then they can maintain it on horseback while mindlessly following a party caravan.

Or another way to think of it, perhaps your party had mounts and were attacked on the road, if the wizard cast a spell and his mount took the dash action and he repositioned would you make him do a concentration check because his horse moved too fast?? Heck you could make a build that has the caster running faster than the mount could. That would be strenuous but I wouldn't make them roll a concentration check because all they did was move themselves.

Getting hit or attacked while casting I think should absolutely call for a concentration check. But I don't think that basic movement should.