DEAR MISS MANNERS: If I invite someone to join me for an event via text or email, and they haven’t responded, how long should I wait before inviting someone else? Sending a casual invite with a deadline doesn’t seem very personable. If I move on to another person, should I let the first choice know? If so, how can I phrase it without sounding like I’m chastising them for not responding promptly? What if the timeline is tight, like I won concert tickets for this evening and I’m looking for a companion? Is it okay to invite multiple people and let them know that the spot will be filled by whomev…