Filtering: need one sample per minute, but have irregular time intervals

[shredr]

Afternoon....

I am doing several oven temp analysis over the next couple weeks.
My data is coming from two instruments, and I need to merge results to compare.

One unit I can control the time interval, and have it set for once a minute, ez pee-zee
The other one...well I get what I get, and it's chapping my hide at the moment.

I need to extract one data set per minute, which one's not important.
Some minutes have two samples, some three, some four; there's a 40 second interval that skews everything

Hoping someone here has a simple solution, I need to do this for about a dozen ovens.

Thanks
Ted

Here's a small data set (actual file is about 4000 rows deep x 16col wide, but I'm going to have some that are 10000 rows)
The left column is what I get from the export, I added the right one to see what was going on, 40sec interval shows up every 18th row

time interval
14:50:58
14:51:08 0:00:10
14:51:38 0:00:30
14:51:48 0:00:10
14:52:18 0:00:30
14:52:28 0:00:10
14:52:58 0:00:30
14:53:08 0:00:10
14:53:38 0:00:30
14:53:48 0:00:10
14:54:18 0:00:30
14:54:28 0:00:10
14:55:08 0:00:40
14:55:18 0:00:10
14:55:48 0:00:30
14:55:58 0:00:10
14:56:28 0:00:30
14:56:38 0:00:10
14:57:08 0:00:30
14:57:18 0:00:10
14:57:48 0:00:30
14:57:58 0:00:10
14:58:28 0:00:30
14:58:38 0:00:10
14:59:08 0:00:30
14:59:18 0:00:10
14:59:48 0:00:30
14:59:58 0:00:10
15:00:28 0:00:30
15:00:38 0:00:10
15:01:18 0:00:40
15:01:28 0:00:10
15:01:58 0:00:30
15:02:08 0:00:10

EDIT:
It gets worse....it arbitrarily starts sampling every 10sec about 2000 rows in

Has Skynet activated itself???

 

[shredr]

Anyone have a pointer on this? I'd rather not have to go thru thousands of rows deleting if I can help it

Thanks
Ted