You can set the date with dashes (2018-01-31) and the time with a 12-hour format (04:59PM), but you can change these formats in your company settings, at all times.
You can see the date with forward slashes (01/31/2018) or fully worded (January 1st, 2018) and see the time with a 24-hour format.
Both displays for the date and time will be effective for every user in your account and, if you insert any custom attributes containing a date or time in your messages, they will appear as chosen in your company settings.