Okay, critiquing here can get tough... The fact is, you've got a low frame-rate operation, so it's bound to be a little slow and even choppy. It's not a crippling problem, but you do have to focus on other aspects to get the audience to invest (emotionally) or you're just going to come across as "meh"... And frankly, that kind of happened here.
You've got good clear audio, reasonable and fun sound effects, and even the electronic voice was understandable as well as humorously holding a purpose. All this along with decent quality art is good.
A sight gag about a timebomb isn't so much difficult to make comical, as it gets a little involved in a few essential questions. You don't get laughs by just blowing up a main character. You've got to build up to that for it to be funny... The essential questions and the answers you create in the video are how you build to the bomb becoming a punchline instead of just blowing up a teacup that virtually no one will care about.
1. Why should we care? Yes, the teacup is alive, but it's still just a cartoon cup of tea. Cartoon characters have been getting blown up for ages, and they generally fare pretty well through it... So we (audience) need some reason to be involved in this story.

2. Where's the motivation? Does this teacup have enemies? Or is there some international conspiracy to deprive the rest of the civilized world of tea. Yeah, it relates to question one, but without some identifiable motive, there's no point. Is it a prank, or a crime? You can present the international conspiracy with a newspaper headline (or even a few)... just for a possibility.

3. Who would you call about a bomb with less than fifteen seconds? It's mostly only essential (as specific as it is) because that was dictated in the vid'... Most generally regarding a phone call, who do you call in the time allowed? The point here is that the gag revolves around a phone call, so someone would have to have a chance at a solution for the problem with the phone... or there needs to be a better explanation for the call in the first place. At fifteen seconds (considering response times from most common police departments) the best call would be a wife or lover or kids... say good-bye... and... er... well, what kind of joke are we making here? I'm cool with morbid humor, but it tends to generate lots of hate-responses in the comment section... (and those can get carcinogenic enough... right?)
Okay, you've got talent, and some real skill. You can develop the work to do something really great. I hope to have helped you. And I know, there's quite a bit to digest up there (^)... So don't forget to breathe, relax, even jot down a few notes... And keep on keeping on. I believe you can get there from here... It's just going to be a little work.