Converting 23.97 fps to milliseconds for closed captioning

Hello all --

First time using the forum. Hoping you can help. None of the existing threads quite address this need and I've google everywhere to no avail. I have a spread sheet (attached) listing in and out points for closed captioning for a video. The data that my system spits out is:

hours:minutes:seconds:framerate. The frame rates is 23.97. (commonly simplified to 24fps)

The spreadsheet looks like this.

Sequence In Sequence Out Text
00:00:03:15 00:00:04:14 Since this morning
00:00:04:15 00:00:05:17 I’ve been standing by
00:00:05:18 00:00:07:04 this road, waiting for a truck
00:00:07:05 00:00:08:06 for my little boy, who goes

I need to to convert all the time codes into:

hours:minutes:seconds.milliseconds

--with a period separating the milliseconds
--milliseconds to the 3 decimal place.
--Example: 00:00:07.430


For the record, this is to fulfill the data requirement for youtube closed captioning .srt files.

Frame Rates of Various formats (found these numbers here)

Name Standard Fps FFmpeg
Movies NTSC 23.976 24000/1001
Movies Quick time N/A 29.976 10000000/417083
TV Video NTSC 29.97 30000/1001
Movies PAL 25 25
TV Video PAL 30 30

It would also be useful to be able to do this for 29.97 fps (commonly simplified to 30fps -- although PAL is true 30fps)

What formula could I use in my Excel Mac:2008 that would convert all this data?

Note: this old program that does what I'm asking for found here (http://www.belle-nuit.com/timecode/) does not work for me. Too old and no updates.

Thanks so much in advance! Let me know if I didn't make anything clear or failed to provide enough info.

Jimbo