Q7 – Incorrect!
You should use; “Samples were removed at various times.”
Various means that there were multiple timepoints that samples were removed at. Varying means that you changed the collection timepoints (sounds like you changed it every time… sounds haphazard!)
Note; a better phrase would be: “Samples were removed at predetermined times”
Realistically, you should say what the specified times were! Don’t be vague!