Moving average if the difference between two date-hours is less than value

I have a dataset in Excel consisting of 800,000 rows with data, there is registered a value every 4 minutes. I would like to do a moving/running average where I look across 3 hours (so 15 rows of data). However due to outages and other unforeseen events, the data will quite often have a lot times where the is a much larger time between registrations, perhaps hours or days.

I'm trying do the 3 hours moving average but only if the difference between the last items in the running average has a time difference less than 3 hours. If the time difference is above 3 hours, it needs to start a new running average from that value. Is this possible using Excelformulas?

I've added a sample data below, covering column A and B.

Date/time	Data
06-09-2017 18:25	1,473
06-09-2017 18:29	1,488
06-09-2017 18:32	1,537
06-09-2017 18:36	1,66
06-09-2017 18:41	1,863
06-09-2017 18:45	2,124
06-09-2017 18:48	2,364
06-09-2017 18:53	2,57
06-09-2017 18:57	2,723
06-09-2017 19:00	2,853
06-09-2017 19:04	2,959
06-09-2017 19:09	3,082
06-09-2017 19:13	3,246
06-09-2017 19:16	3,47
06-09-2017 19:20	3,699
06-09-2017 19:25	3,883
06-09-2017 19:29	4,001
06-09-2017 19:32	4,025
06-09-2017 19:36	3,942
06-09-2017 19:41	3,772
06-09-2017 19:45	3,564
06-09-2017 19:48	3,323
06-09-2017 19:53	3,075
06-09-2017 19:57	2,842
06-09-2017 20:00	2,64
06-09-2017 20:04	2,475
06-09-2017 20:09	2,347
06-09-2017 20:13	2,257
06-09-2017 20:16	2,209
07-09-2017 20:20	2,21
07-09-2017 20:25	2,23
07-09-2017 20:29	2,225
07-09-2017 20:32	2,169
07-09-2017 20:36	2,069
07-09-2017 20:41	1,938
07-09-2017 20:45	1,797
07-09-2017 20:48	1,657
07-09-2017 20:53	1,521
07-09-2017 20:57	1,401
07-09-2017 21:00	1,289
07-09-2017 21:04	1,187
07-09-2017 21:09	1,097
07-09-2017 21:13	1,017
07-09-2017 21:16	0,948
07-09-2017 21:20	0,889
07-09-2017 21:25	0,839
07-09-2017 21:29	0,795
07-09-2017 21:32	0,757
07-09-2017 21:36	0,721
07-09-2017 21:41	0,688
07-09-2017 21:45	0,656
07-09-2017 21:48	0,625
07-09-2017 21:53	0,595
07-09-2017 21:57	0,566
07-09-2017 22:00	0,539
07-09-2017 22:04	0,511
07-09-2017 22:09	0,487
07-09-2017 22:13	0,475
07-09-2017 22:16	0,468
07-09-2017 22:20	0,461