I'm not at all convinced this is an issue with subscribe2, but for what it's worth:
When I use the command-line tool:
wp post create
I would expect that the emails get sent as indicated in the same command. Instead, the emails get sent immediately. It's probably important to note that the post itself also gets published immediately (which in turn means that the emails get sent).
I spell this out more fully here, with reproducible error:
Thanks for any help.