Sub after timeout

[just another ref]

My small association has been absorbed this year by a larger association so I find myself in the role of "new guy" for the first time in quite a while, which is not what I do best. But with that in mind, I err on the side of caution when dealing with a veteran official who I am working with for the first time. We are shooting two free throws and home team calls timeout. After the warning horn at 15 seconds, sub reports for home and he properly says she must wait. I'm C. After the first free throw I look expectantly toward the table and.......nothing. I blow the whistle and point. Partner at T shakes his head. I walked over and asked what the problem is. He says after a timeout a sub who reported after the horn can't come in until after the clock has run. I tell him no, that the timeout is over and the sub can enter before the last free throw. He was adamant, he was the R, and it was his sub so I backed off. Between games he rooted through the rule and case books but "couldn't find what he was looking for." He promised to finish checking it out and get back to me. He said "I may be 100% wrong but I've been doing it that way for a loooong time." (I don't think he believed he was wrong) I told him he was confusing this with the player returning who had been subbed out.

I'm also 100% sure that I'm right but there's comfort in numbers. So, go ahead guys. Back me up and share your thoughts on a veteran official making this kind of mistake.