You are sending collection times to several people who do not know one another. Putting their addresses in To or Cc lets recipients see the list. Bcc is useful when each person needs the notice without receiving everyone else’s address.
Check the fields in the final draft
In Gmail, Bcc recipients can see the people in To and Cc, but not the other Bcc recipients. The sender still knows whom they included. Hiding addresses does not prevent a recipient from forwarding the message or sharing its contents.
For a harmless rehearsal, use accounts you control. Put one in To and another in Bcc, then inspect the received copies. Check the actual address fields, not just the names displayed in the message list. Google notes that other mail applications may not show a clear indication that a message was received through Bcc.
Reply All is not a promise to include the original audience
An ordinary recipient’s Reply All does not bring the hidden Bcc list into the conversation. Someone receiving a Bcc copy should also inspect the outgoing recipients before replying: their own reply can reveal that they received the original message. The important check is who will receive the next message.
For a simple announcement, Bcc can keep the address list out of recipients’ copies. For an ongoing discussion, agree on an explicit group of participants instead of assuming everyone follows the same thread. Before Send, check both the address fields and the body. A hidden recipient list does not make personal details in the message confidential.