Guys, I was leery about the timer too, at first. Then I played the game... it made for some exciting/tense moments that were really awesome. Like, "Ah! The day's ending, and a pikmin somehow got left way over on the other side of the map! I must save the poor little bugger!" So you put the rest of your pikmin in the onion (their home) and race off to get the little guy. Chaos/drama/excitement ensues... but in a fun way!
And if you're worried not about the day-timer, and more about the 30-day limit, don't be. There're more than enough days to explore to your heart's content and still beat the time limit. As you get used to the system, you'll be getting multiple parts per day much of the time, leaving days just for exploring fun.