XY graph time abscissa in days problem

[gnappo]

I have to put on the abscissa the day number of the experiment. 

So I put in the formatting the following string <%D>t in order to have the day number. Unfortunately what I don't like is the x markers are not separated by 24 hours among them and I have some ugly results, where, for example, I see on the graph the same number repeated for some days, that is, for example ...12,13,14,15,15,16,... 

Can you help me to force the markers to be put every 24 hours or a multiple (48 hours for example) ? 

Thank you

[Dennis_Knutson]

We need to see sine code. It sounds like you are taking multiple samples per day so the x axis is expected.