I'm really lucky.....I bring both Callan (7 months now) and Indy (6 years) out at the same time
Indy would rather NOT do his business if Callan is around, so he normally just sits and waits his turn (who needs a puppy sniffy up your butt while you are trying to pee!)
So our latest routine is this. 6 a.m. Both boys get fed. 6:10 Outside. Callan pees and poos immediately. Indy not. I bring them both inside and then Indy is let out again to do his business in peace.
After that.....Indy is a camel.....he can probably go 24 hours if necessary! Callan will pee everytime he sees grass. Poo is now down to only twice per day, but not predictable. Sometimes in the late morning, sometimes early afternoon, sometimes evening.
Only bad news is that Callan will NOT pee on a leash. Neither will Indy, but because he can hold it FOREVER I don't worry about it. But I bring both dogs to my store often, and take them outside regularly to the regular pee spots, and they just sniff.
Annoying!