I have cobbled together Chip Pearson's code for running an macro queries of
Yahoo Finance for stock data (code also borrowed). Here's the basic structure
so far:

Public RunWhen As Double
Public Const cRunIntervalSeconds = 120 ' two minutes
Public Const cRunWhat = "GetData" ' the name of the procedure to run

Sub StartTimer()
RunWhen = Now + TimeSerial(0, 0, cRunIntervalSeconds)
Application.OnTime EarliestTime:=RunWhen, Procedu=cRunWhat,
Schedule:=True
End Sub

Sub GetData()
<my code
StartTimer
End Sub

There is also another generic piece of code courtesy of Mr. Pearson:

Sub StopTimer()
On Error Resume Next
Application.OnTime EarliestTime:=RunWhen, Procedu=cRunWhat,
Schedule:=False
End Sub

...but it is not currently being called.

I want to 1) GetData (see above) between 9:00 and 15:30 daily only (this
spreadsheet will reside on a dedicated computer, hopefully always on), and 2)
perform other macros at, say, 8:30 and 16:00 daily. I am uncertain how these
last two items get coded. Any help appreciated.