my sheet contains rtd [....] the need is to have this formula to run at, eg, exactly shift startup or as close to that time as excel can determine. be that 1/100 second before the specified time or 1/100 second after. [....] does that help?
Yes.
Not to nitpick, but in the interest of clarity.... Since NOW() is a "volatile" function, any formula that uses NOW() or that depends directly or indirectly on a formula that uses NOW() "runs" (is recalculated) whenever any cell in the workbook is modified (by RTD, for example), not at a particular time of day.
So I assume that we are still talking about a formula of the form =IF(A1
> A2,B4,C6), where A1 is current time, and A2 is the shift startup time, for example.
(Do you really mean =IF(A1
<> A2,B4,C6)?)
You say that "1/100 second before" or "1/100 second after" should be considered "equal". I hope that 50/100 before and after is just as good.
In that case, instead of =NOW() in A1, use =--TEXT(NOW(),"h:m:s").
That captures the current time (at recalculation time)
rounded to the second.
And =IF(A1 > A2,B4,C6) should be sufficient, assuming that A2 is also rounded to the second, as it is in your original posting as a result of =TIMEVALUE("9:00:00").
Note: I use "h" instead of "[h]" so that 23:59:59.500 is rounded to 00:00:00, which is how midnight is written in Excel, not 24:00:00. But that might be something that you need to think about.