If you're happy with the rates, it's generally a good idea to lock them in while you still can - because they can and do change daily. If you don't act on the same day quotes are generated, there's absolutely no guarantee that the same rates will be available the next day.
With that being said, price isn't the only factor to consider. You should also think about what you get for your money. Of course, this all depends on your circumstances. Very few people spot the best rate from searching a single site alone! One of my best tips is to compare all your options across multiple different tools first. If you do that, you'll get a much better picture of the market. Saying that though, it's also down to your own judgement. But for me personally, I've found that the cheapest deals tend to be linked to poor service (but not always). Especially important to consider that fact! Such tempting deals are often a bait and switch most of the time. To be honest though, now is probably not a good time for 24 month deals, because the market prices could well drop by this time next year.