This is really good. I love the emotion that you've obviously added into this, your feelings and thoughts come across so clearly in your words and I really feel I can relate to everything you're saying here. I think everyone can think back to a time in their life when they've felt everything that you've described in this and I think it's fantastic that you've taken such a simple concept and turned it into something amazing.
Your word choice is really lovely too. I adore the repetition of tick-tock between the stanzas, it ties everything together perfecty (and I'm a massive sucker for repetition in everything). Again, like your concept, the language is very simplistic and that works so well in drawing the reader in. You've used language that any child or teenager can easily understand but it really adds to the piece as a whole and I really think that's one of my favourite things about this. It doesn't try and embellish, it just states it as it is and I think there is a serious lack of pieces like this on Mibba.
This is among my favourite pieces of poetry (granted, I don't have many) and I'm glad you gave me this to comment on. No grammar issues, no spelling, just good, honest writing. I love it.