Test this one

(Not Tested)
Code:
#include <amxmodx>
#include <amxmisc>
public plugin_init() {
register_plugin("TimeandDate", "2.0", "SuperMan1337")
set_task(1.2, "UpdateTime",_,_,_,"b")
}
public client_authorized(id) UpdateTime(id)
public UpdateTime(id) {
new Time[64], Date[64]
get_time("%H:%M:%S", Time, 63)
get_time("%m/%d/%Y", Date,63)
set_hudmessage(255, 255, 255, 0.5, 0.93, 0, 6.0, 1.0)
show_hudmessage(id, "The Time: %s\nDate: %s", Time, Date)
}