時間refers to the concept of time or a specific duration. It is used to count hours when combined with numbers (e.g., 1時間for one hour). While 時refers to a specific point in time, 時間focuses on the interval or the resource of time itself.
That is how Fuguro works. It brings 時間 back for review right before you forget it, each time a little later, until it sticks for good. You hear it spoken aloud, and you meet it again in stories you can already read. The first five levels are free.