Modern Events Calendar time format is available in two models. You can in three steps change the time format into your preferable one.
Here we can see a conversation from the Modern Events Calendar’s support desk which is about Time Format

MEC User
Hi! I can’t find where to change the time of the event from 12 hour to 24 hour format. In the attached link you can see that it uses 12 hour format. Where is the option to change it?
URL
Hello,
You can go to WP dashboard > settings > general and from there change the time format.

Support Staff

MEC User
And how can I change time format on single event page and shortcodes?
URL
You can change the date format on shortcode settings.
And for single event page you can change it on settings.
Regards,

Support Staff
Hi there
Just started with this plugin. So far I came across a critical issue. Is there really no way to use 24 hours format within the calendar? The time format in wp is set to 24 hours, but I can’t find it anywhere in the Modern event calendar. I need to know this before investing in the pro version and the Elementor integration. Look forward to hearing from you. Thanks, Xander
Our plugin follows the time format set in your WordPress back-end setting, so please change your time format as desire and the changes will be made. If you are not able to follow this instruction, please submit a support ticket and we will guide you trough.