Formular to calculate how many instances of cells with time within 7:01 AM to 7:30 AM

I have a work schedule for my employees, where I want to have an overview of how many at work at 7:30, at 8:00, at 8:30 etc.
Years ago I got help in here to calculate how many instances of "7:30" is found within a given cell range.
But now I have to have varied meeting times, so if someone has a 7:45 meeting time, it won't be noticed by the system. Can I have it check for all times between 7:01 to 7:30 AM? Then I know how many are at work at 7:30.

I use this formular now:
=COUNTIF(G$4:G$15, "7:30")+(G18)

You can make a copy of this Google Sheets (which I work in, not Excel but hope the formular is the same) and try it yourself, if you know a solution:
https://docs.google.com/spreadsheets...it?usp=sharing

Beneath the work schedule, is the cells where I would like to see how many are at work at 7:30, and further down is shown how many is left at work at 15:30 e.g.

thank you in advance, if possible.

Greetings, Jamie from Denmark

Wouw... That is so sick. It is perfect! When I look at the formular, I don't even understand what it does.

BYROW is a function that just avoids you having to place a formular in each cell in the column, so it makes it easier for edits, right?

LAMBDA, what does that do?

starts and ends - I dont understand what this refers to, probably the following part (which I don't understand either). How does it know, what range I want - in the BYROW cells, there is text and numbers, so it can't get "7:30" from that, I suppose.

The >= division of the formular I also dont understand.

REGEXEXTRACT Ah, this one extracts part of a text, but the cells doesnt say start or end anywhere

The slash b slash d 1,2 etc, I don't understand that either.

You don't have to, but out of curiousity and if I should make or edit this formular myself sometime, if you have the time can you then explan the formular from the >= and REGEXEXTRACT and onwards?

Well, thank you so much for saving me time! Not back to fixing the whole in the work schedule, after a newly recruited employee left for another job, three days before the two teambuilding days I planned for the new team on monday! Mine was temporary and she got a lasting job, so understandable.