Hi Daniel,
Thank you for using Syncfusion products.
We suggest you to use the DateTimeFormat property of the Primary X axis to format the datetime value of the Chart Axis labels.
Please refer the documentation from the following link:
http://help.syncfusion.com/ug_83/User%20Interface/ASP.NET/Chart/default.htm?turl=Documents/axislabeltextformattingappearanceandpositioning.htmLet me know if it helps.
Regards,
Jaffer