IMHO, him getting angrier is EXACTLY what you want when you put a child in timeout, especially in the beginning. If my son wasn't crying unhappy, or screaming mad when I put him in timeout... I guilted him into being unhappy. Now, I didn't yell or do anything mean (in fact, if I was losing my temper I went outside and took my own timeout until I could be calm and matter of fact, before I talked with him), but I definately wanted him to be feeling lousy. Also, so he wasn't just focused on how HE was ticked off, I'd remind him every minute or two WHY he was on time out ("You're on time out for *HITTING* your mommy. It is NOT OKAY for you to be hitting people because of ________. You don't HURT the people that you love, on purpose.").
ONLY after he had calmed down AND we had talked it out (why he was in time out, why what he had done was wrong, and what he could do INSTEAD of the offense next time -which means tracing back the "why x happened" in the first place) was he allowed to come out of time out.
Most kids aren't born with empathy (although some either are, or pick it up from example very very young)... but for most we have to teach them to feel badly about their actions that hurt others (after all, hitting doesn't hurt the hitter... and if they get what they want from the situation, bonus!)... which means that they DO actually have to be unhappy. The unhappiness usually starts out as personal affront. and then we link it to the offense, but constant repetition. Kinda like Pavlovian training.
When my son was 2 timeouts were no problem (for one thing, timeout was in his crib). When he was 3 through, we'd have days where he might be in and out of time out 2 times an hour all day for 3 or 4 days in a row. Oy. (Can you tell we had the Terrible THREE's in our house?). Then it would be good behavior, mostly, for a week or so...and then back in and out of timeout. When he was 3.5, we finally got rid of the crib, and had a new problem: staying in timeout.
Most of the time, the whole leading them back to the room (hallway/couch/staircase/whatever) silently was sufficient. Once though, in a towering rage (I was really tempted to put him in a cold shower to cool off...would have if he was older, but I was afraid he'd hurt himself), I had to literally sit beside the door to his room. When he started to try and rip the door off it's hinges (kinda cute in a 3 year old), and then started opening it and slamming it into the wall and doorframe, he got a warning that if he did it again I was going to hold the door shut. I held the door shut for 20 minutes while he thrashed himself out (totally safe room to do it in). My heart was breaking the entire time... but this whole thing had become a Big Deal. Any attempt at calming him merely erupted new fury (awww, poor little love... and poor me!) Anyhow, I'd committed myself to the battle (I pick mine rather carefully, since my parents never picked theirs)... and there was no way I was going to back down and teach him that if he got REALLY angry he'd get what he wanted.
That "coming off of time out" conversation was a long one. Not only did we have to discuss what had started it, but we had to talk about what had happened DURING it, and that he *needed* to listen to me. That timeouts aren't punishments, they're a time to cool off and either get our tempers back or think about how to fix a problem that we had created. Discipline, as opposed to punishment.
We never had a problem again, though, with him trying to leave timeout early.
We haven't had the multiple timeouts over multiple days thing since his 4th birthday (thank god). At most it went down to 1 every week or two. He also started putting himself in timeout (house rule, if you put yourself in timeout *before* losing your temper you can come off whenever you want... and you only have to talk about it if you want to.)
These days (7yo), I end up putting him in timeout maybe once a month... and I've "banished him to his room, in disgrace" (which is way different that time out) twice in the past year.
Another rule, that works in our house, you might think about ... is what to do when someone throws a fit. in our house "If you throw a fit, you don't get what you want" hands down, flat out, always (there are way better ways to get what you want)... AND it also equals timeout (for a month he tried throwing a fit whenever he wanted alone time, and that had to get nixed... but it was a quick fix).
I know a lot of parents hold out a reward for stopping the fit (aka, they can have "x" once they've calmed down)... but since we have hot tempers in our family... it's been more important for US to teach how to deal with tempers (aka, you NEVER get what you want when you throw a fit) than to smooth the waters, or bribe our way out of bad behavior. <grinning> We DO use bribery, but only for good behavior. Not returning to good behavior.
Anyhow, as always, just what's worked for us.
:)