If you've ever read or seen Maid-Sama, you know what you are getting here: nerdy girl has a secret job, popular boy finds out about it, romance ensues.
Naisho no Jikan isn't as good as Maid-Sama, mostly because it's truncated length doesn't allow for much exploration of the characters or their relationship; but for a one volume shoujo romance, it's still pretty solid.
Story (8): I'm a sucker for this kind of story vanilla romance, and this is an above average version of it. The only problem with the story is that it is rushed; five chapters really isn't enough time to get to know
the characters very well, and their relationship moves at light speed. Still, if you like a good vanilla romance, the story is quite serviceable.
Art (6): The artwork I found a bit lacking. All of the characters looked appealing... but the main girl's cosplay look was TOO different from her normal look; it didn't look like the same person wearing different clothes and wig, instead it actually looked like two completely different people.
Character (8): I really liked the characters here. Both Mahiro and Hinata are likable characters that make sense as a couple. I would have loved to spend more time with them.
Enjoyment (8): I really liked this manga; it's just about everything I want in a short, vanilla shoujo romance.
Overall (7): I would have loved Naisho no Jikan were it longer, and could have gone into more depth with the plot and characters. At it's current length, it's solid and enjoyable, but not truly great.