In working an infusion time problem, if you are asked "when" or "at what time", you need to determine the specific time, not just the hours and minutes.  The problem would be worked exactly as previously noted to determine the answer in hours and minutes.  You then determine what time it will be from the given time based on those hours and minutes.

You can simply use your watch and count the time.  However, another way is to use military time and add.


For example, if you have determined that an IV will last 3 hours and 24 minutes but you need to know specific time.  Assume current time  is 7:30 am (you will be given a time in the problem).  You can use your watch and count 3 hours and 24 minutes from 7:30, which will be 10:54 am.  This is relatively easy when you have short times; however, longer periods may be a little more difficult.  This is where using military time may help.


Example:  6 hrs and 43 minutes from 2:15 pm.  2:15 is 1415 in military time.


    1415
 +   643 (for the 6 hours and 43 minutes)
     2058

You can leave 2058 as the answer or you can put 8:58 pm.


Example:  10 hours and 35 minutes from 0730.

     0730
  + 1035
     1765

In this instance you have to remember there are only 60 minutes in an hour.  So once the minutes went over 60, it goes to the next hour.

    1765
    -  60 
    1805  (taking away the 60 minutes, but adding it to the hour)


Likewise you have to remember there are only 24  hours in a day. 

Example:  4 hours and 25 minutes from 11:15 pm.

  2315         2730
+  425      - 2400
  2730         0330 the next day