Email Campaigns: How to add Contacts/Leads and when are they sent?

I’m interested in using Email Campaigns to send “drip campaigns” of emails to Contacts/Leads.

I’m confused by how to add the Lead/Campaign to an existing Campaign. From what I can see, it looks like I’d have to create a new campaign (even if it uses the same series of emails) for each Contact/Lead I want to send emails to. Is that correct? Or is there a way I can add Contacts/Leads without having to create a new Campaign each time.

Also, when are those emails sent? I asked the question in the past, and a user said they’d be sent at Midnight. If that’s true, that’s certainly not ideal, and actually quite horrible, because many people would end up getting woken up by phone alerts when they get that email…