Date and time problem

Hi,
I have studied all help I can find but I gor stuck in this – how to change date and time in an appointment form.

The form is:
============================
<p>Ditt namn *
[text* YourName 25/40]</p>
<p>Ditt telefonnummer*
[text* YourPhone 25/40]</p>
<p>Önskad dag och tid*
[text Date 25/40 class:datepicker class:bookform_date "Datum"][text Time class:timepicker class:bookform_time "Tid"]
<p>Annan information
[textarea Info 5×5 ]</p>
[submit “Skicka förfrågan”]
=======================
I would like to use: d M y and military time, eg: 15.30 instead of 3.30 PM.
Please help me out here.
Best regards,
Ulf Selstam

https://ww.wp.xz.cn/plugins/contact-form-7/