I think the problem that you are having is you started by thinking about how you are going to accomplish what you want instead of thinking about what you want to do. Who said anything about Shift Registers? [That's a "how", as in "how do I do this", detail].
When I look at your code, I see a giant While loop with all kinds of things taking place every time the loop runs, so the loop does basically the same thing over and over. I'm sure that's not what you want the program to do. I also see various things all "happening at the same time" (because they are all in the same While Loop with no clear "time ordering" (Do this first, then do that, then do this other thing)).
You will have a much easier time of it if you redesign your program to be a State Machine. You (mentally) divide your program into a set of "States", one of which is "Initialize", one of which might be "Check if Send E-mail", one of which might be "Read Instrument", one might be "Clean up and Exit".
Under what conditions do you want to "Send E-mail"? Better question -- under what conditions do you not want to send E-mail? Sounds like the answer is "Everything is OK" or "I already sent one less than X hours ago". Those are two separate conditions -- one is governed by a Boolean ("Everything OK"), the other by a Time (when was the last E-mail sent). Let's put both the Boolean and a number representing the time of the last sent E-mail in separate Shift Registers. Somewhere along the line, you need to initialize the Shift Registers -- in a State Machine, you do that in the "Initialize" State -- we'll initialize "Everything OK" to True, and "Last E-mail Set" to 0.
As State Machine runs, at some point it might figure out that things are not OK-. You need two States, "Do Main Operation" and "Check Everything OK", where "Do" always does "Check" next, and "Check" usually does "Do" next. "Do Main Operation" does its thing, and reads some instrument to decide if things are OK. If so, it leaves "Everything OK" alone, otherwise it sets it to "False" and calls the next State, "Check Everything OK".
"Check Everything OK" looks at "Everything OK". If it is True, it is done, so it sets "Do Main Operation" as the next State. Otherwise, it looks at how much time has elapsed since it sent the last message (conveniently saved on a Shift Register). If it is "too soon to send another message", it does nothing, and goes back to "Do Main Operation", otherwise it (a) sends an E-Mail, and (b) saves the Current Time in the "Time of Last Message" Shift Register.
I suspect this might be more than you can handle, for which I apologize. I wrote a little discussion of State Machines and what I called the "Boss-Worker Design Pattern" here on the Forums a few days ago, submitted by "taylorblack" on 12 Apr 2023. That has a small example I wrote that has a little State Machine that you can Start and Stop (which was his question), but you can easily adapt this model to not respond to Front Panel Controls (which is what taylor wanted) but to respond to "Everything OK" saved in the Servant Loop.
Anyway, I've been typing for a while, so I'm going to go get some sleep. Learn about how to create State Machines in LabVIEW (While Loop with a Case Statement "fed" by the States you want to run). I apologize for wearing my Professor Hat so much.
Bob Schor
