The late-great monkee & I used to go round & round on what is proper protocol with these drafts. That was a long time ago, and he & I definitely made peace by the time he climbed that great e-tree in the sky... With that being said, I'm going to offer my completely unsolicited opinion.
On one hand, I think that as long as you make your pick before your time slot is up, you're fine. That is, after all, why there is a schedule in the first place. I don't feel insulted or disrespected because the guy that had a draft slot at 2pm makes his pick at 2:55pm.
That said - it really IS annoying when you're scheduled to pick at a time that is terrible for you (while you're typically asleep, at work with no access, class with no access, etc) and there's one guy that holds things up. It's cool if it happens occasionally, but when the same person continues to hold up progress over & over, it becomes extremely annoying.
I myself detest sending proxies. I hate giving anybody a gleam into who I'm looking to pick. Sometimes, you could have ended up getting multiples of the guys you proxy. Also, sometimes you are 8-12 picks away when you know you're going to be MIA for the next few hours and can't really make a good list. What I've done in the past couple of years is send a single proxy to the next 2 behind you with the instructions that if the player is taken, then the league will just have to wait for you to make your own pick. Sorry. Most of the time, I get my guy when I do this. I'm not sure I've ever held the league up when I did this, but if I did, hey, I made an effort to keep things moving. If anybody has a problem with that strategy and/or attitude, then tell them to feel free to pay for your team.
That's the bottom line IMO. I don't want anybody held up by me to feel disrespected, but in the end, this is a competitive thing... that (in general) costs money. For my $10, you can bet your *** that I'm going to do my damnedest to make the best team possible. If that causes someone to be delayed 2-3 hours, too bad.
Of course, something else you can do when you know you're going to be REALLY busy during draft week is to skip this round of the league and rejoin later when you will have more time...