Yes, the concentration of the sucrose solution. Yes, time for crystal formation. Yes, the control could be one of the sucrose solutions. Yes, controlled variables are such things as the temperature and light in the room, containers the crystals are grown in, etc. V. Data Data is the only way that a judge has to determine whether or not you did an experiment.
Judges like to see tables, charts, or graphs of the measured results.
Any project that has data generally gets an automatic second look by judges. If there is no data, judges start to look for the reason why, and they usually conclude that the student doesn't understand what an experiment is or how to do one. Once you have decided on your project question, your hypothesis, and basically how you are going to test your hypothesis experimentally and record data, then start your project by designing the experiment step by step. Do perform the experiment four or more times. For the sucrose crystal example, instead of making each solution four times, you could make four times as much of each concentration and pour it into four separate containers.