Thanks much for your response. I installed the SMS Scheduler app to be able to send scheduled SMS messages, as that capability does not work in my messaging app.
I know the flagship app of Gizmoquip, the group that wrote SMS Scheduler, is "SMS Tracker", which is designed to be the sort of app you describe, one that can be installed without a user necessarily knowing it and track information. They are quite open about that, as they sell it for tracking one's children.
The SMS Scheduler app is a separate app from that, one of a few others besides the tracker they have released.
Is the SMS Scheduler being tagged as spyware in "guilt by association" because it is made by the same group that makes SMS Tracker? Or does it have its own spyware built in? If I whitelist it, just what am I whitelisting? According to Gizmoquip's support response, it is not a virus or malware. I have asked a few more specific questions of Gizmoquip, but it seems to me that Malwarebytes could also be more forthcoming about the details of just why they tagged this particular app as spyware.