Incorrect bar positioning with time scale

[Milabrega14]

I encounter strange behaviors with time scale even in the most basic of setups.
For example, in the following jsfiddle, i simply want to display a few bars that i define manually. Nothing too fancy:

https://jsfiddle.net/dapg2b4r/

The bars supposed to appear at 08:00, 16:00 or 18:00 are not positioned correctly.

I understand the time scale feature is being worked on and needs improvement, so i'm not sure exactly what my expectations should be for this issue. Could someone shed some light on this behaviour please?

Is there some way to get a more reliable result? (or maybe something is wrong with my code?)
Thanks for any answer.

[simonbrunel]

This is fixed in master and will be available in the next release (fiddle)

See #4994