Count overlapping times on a moving 30 min window

[kbrono]

I searched the forums for a similar question and did not see one that helped with this question.

I need to know on average how many airplanes are on the ground at the same time during the day.

To get an accurate number it needs to look 30 minutes ahead of and behind the departure time and then count how many other departure times fall in that window. Here is a sample set for two different days.

Day	Equip	Dept Time	Total Departure	Dept Hour	Staffing
1-Sep-16	CM9	6:43	1	6	4
1-Sep-16	CM9	7:00	1	7	4
1-Sep-16	CM9	7:45	1	7	4
1-Sep-16	CM9	8:05	2	8	8
1-Sep-16	CM9	8:10	1	8	4

<colgroup span="3" width="137"></colgroup> <colgroup width="154"></colgroup> <colgroup span="2" width="137"></colgroup> <tbody>
</tbody>

<colgroup span="3" width="137"></colgroup> <colgroup width="154"></colgroup> <colgroup span="2" width="137"></colgroup> <tbody>
</tbody>

2-Sep-16	CPJ	8:45	1	8	3
2-Sep-16	CPJ	9:15	1	9	3
2-Sep-16	CPJ	10:20	1	10	3
2-Sep-16	CPJ	10:30	1	10	3
2-Sep-16	CPJ	12:46	1	12	3

<colgroup span="3" width="137"></colgroup> <colgroup width="154"></colgroup> <colgroup span="2" width="137"></colgroup> <tbody>
</tbody>

So for the first item I should get a value of 2 because nothing exists before 6:43 and there is only one other departure by 7:13 (30 min after 6:43). Now for example sake look at the fourth line. This should return a value of 4 because there is one departure within :30 min prior of 8:05 and one within :30 after 8:05 (there are two departures at 8:05).

So when then first aircraft is on the ground there is a total of two but when the 4th is on the ground there is a total of 3.

I then would need it to reset for the next calendar day. I will then take the average for every day for the entire month to say "at any given time there are xx aircraft on the ground at the same time"

The data set i have is a few thousand large.

Thanks,