Hi,
I am afraid that it cannot be done directly. One solution is adding one more layer linked X. The following tips may help.
1. Set two customized format for date and time, such as MM'.'dd'.'yy and hh:mm. You can do it by menu Tools: Options, and then go to the Miscellaneous tab. Please refer to this page for more details.
2. Set tick label by using the customized date and time format, such as
layer.x.label.type = 4; // Date
layer.x.label.timeformat = 20; // the first customized format
This page can help you more.
3. Add one more layer by the layadd X-Function, and then set the tick label as Tip 2 above.
4. Move the tick label position, so to make them look like two lines.
Penn