How to deal with datetime ranges in a table with separate columns for date and time?
You can use the simple condition:

WHERE (ev_date, ev_time) BETWEEN (start_date, start_time) 
                             AND (end_date, end_time) 


or this one:

WHERE ev_date + ev_time BETWEEN start_date + start_time
                            AND end_date + end_time


What's the best of these two depends on what indexes you have on the table. If you have an index on (ev_date, ev_time) use the first. If you can add a filtered index on (ev_date + ev_time), use the second.

*: I'm assuming that all these are parameters: start_date, start_time, end_date, end_time.