Problem with Linear Regression node

Hi guys!
I have a problem with the linear regression node: I would like to see the trend of certain laboratory data in a single day.
I would put on the X axis the analysis time (HH:mm:ss) but the node doesn't accept a non- numeric variable on the X axis.
 

How can I solve this problem?

 

Hi Sandorkan,

you would need to map the time to a numerical value. You can for this use the Time Difference node.

Best regards, Iris

Hi Iris, thanks for your answer.

I tried with the time difference node and this is the result:

http://it.tinypic.com/r/nmagqp/9

These are the configurations I tested:

http://it.tinypic.com/r/21oxydy/9

As you can see I used 0.0.0 but I don't have an accurate difference.

How to transform the time correctly?

And finally, the values ​​are reversed on the graph, how to fix it correctly?

http://it.tinypic.com/r/nzmu09/9

I ask again apologize to all of these questions but I'm really new at this and study different subjects!