Filter and extract data that occurs every 30 seconds.

This is going to take a lot of explaining.

First of all, I converted the data to a table. Tables copy formulas down automatically and formulas can be expressed as column headers so they are easier to understand.

I replaced your second formula with =SECOND([@Time])

I also calculated Date, Hour and Minute using similar formulas.

The main plan of attack is to look at the seconds in groups of minutes. Furthermore, I want to look at zero past the minute and 30 past the minute.

So, I computed two “bases” The Date + hour + minute and the Date + Hour + Minute + 30 seconds. (Columns G & H)

Then I took the absolute difference between the actual time and the two bases. (Columns I & J)

Columns K & L get the minimum of the differences between the time and the two bases.

Columns M & N are what old-school Excel would have called array formulas. That is, they work on an array of cells instead of individual cells. The column M formula is:
=MATCH([@[Zero Sec Min]],IF([@[Zero Base]]=[Zero Base],[Zero Second Diff],FALSE),0)

We will work the formula from the “inside out.” The if statement says look at the rows where the base is equal to the base on this specific row. Ignore all other rows. This array or range limits the Match. So even tough there may be multiple same minimum values for other minutes, match will only find the row for this specific minute.

Finally the formula in Column O is true of the minimum of the zero base or the minimum of the 30-second base matches the row.