chart with some missing points

My boss wants me to prepare a chart for him that has duration of software use on the left in minutes, and dates at the bottom.

So for January my data might look like this:

Day Student ID Duration
1 12345 23
1 23456 12
1 34567 45

3 23456 9
3 34567 25
3 45678 68
3 56789 35

(the 1's and 3's are dates, the 12345 type numbers are student ID's, and the last set of numbers are login durations, for some reason it's not formatting the spaces well here).

And so on. As you can see, some days kids didn't log in at all (weekends, etc.) and on some days, certain kids did log in while other kids did not.

He wants each child plotted, so each kid would be a separate series indicated by a certain color line.

My problem is this: I can't get the line to break where there is no login and start up again for that kid when there is a log in. I also can't get the chart to put the dates correctly at the bottom.

Any ideas?

Thank you!