Comparing events to time intervals

[Lemac]

Hi Everybody,

I have an issue with finding the right visualization for this problem:

I have a department with ~40 Employees. Those employees log in and out of the system: So they have a logged in time. If they take a break, they should log out.

When they are logged in, they can produce crates. Those crates may take between 10 seconds and 5 minutes to produce. 

I want to plot the logged in time during the day and the crates that they produce in some kind of graph. This is to assess whether someone is slacking off for 20 minutes without logging out. I was thinking maybe a kind of bubble graph, with a single bubble for each minute logged in, which is white and if a crate is produced during that minute, it turns green. 

However, the 1000 data-point limitation of the bubble graph makes it unfeasible. 

What I had in mind was something like this:

Intervals and Events visualization sketch

The colored bars are intervals per employee and the bubbles are the arrival times  of the crates they produced. 

Is there a visualization that does this? Or is there another approach to comparing these entities visually that is better suited?