I'm not sure it fits in Testimonials, either, to be honest! Testimonials is "Share the reasoning behind why you believe or disbelieve in a theistic entity", which definitely doesn't fit with what you want to do.
We've had threads before that give sporadic updates on ongoing "projects" - I recall one on giving up smoking, for example, but of course this being a forum they tend to devolve into discussion around the topic.
If you intend it to be a diary, then again I'd strongly suggest you go with a blog site. You would have a better record of your progress, without the forum chatter that goes on. With the best will in the world, threads diverge into ancilliary chat, which is going to detract from what you (I presume?) want to have, which is a journal of your regular progress in a field. A blog will also avoid the situation where you could end up with posts talking about Monday's progress appearing in-thread after Thursday's updates......having just refreshed my memory of the Forum rules, I also suspect that a daily record could fall foul of the rule that "Discussion threads are for discussion of the topic at hand, not simply advertising one's opinions"
For what you want to do I honestly believe a blog would be a better bet - I'd give the same advice to anyone wanting to make a daily (or thereabouts) record of what they are doing.
Greybeard is my co-Mod in Chatter - I'll PM him to get his opinion.