Emails and SMS message seem to have similar 'delivery time ranges' to me. I send this message, and it will arrive somewhere between pseudo-instantly and take a minute.
With my conversations, it is often a minute to get users to respond if they are working on multiple IM conversations and need to finish their thought, or are otherwise doing something meaningful outside of cyberspace anyways, so the delivery time is of less importance.
Boundless speculation: whatever the difference in instant delivery of a message and the human user noting/changing gears to address it and delivery taking (in your worse case example) 1 minute, just in time for the human user to be 'ready' to receive another message is too small to be meaningful for non-techie users.
Anecdata for those users in my contacts list that are techies: after about 5 IMs, further chatting seems to organically migrate to a phone call or desktop client session (Slack/Volt/Skype/Discord) rather than the approx 3 messages every 5 minutes my cursory glance at message times in Signal shows for the non-techie users.
With my conversations, it is often a minute to get users to respond if they are working on multiple IM conversations and need to finish their thought, or are otherwise doing something meaningful outside of cyberspace anyways, so the delivery time is of less importance.
Boundless speculation: whatever the difference in instant delivery of a message and the human user noting/changing gears to address it and delivery taking (in your worse case example) 1 minute, just in time for the human user to be 'ready' to receive another message is too small to be meaningful for non-techie users.
Anecdata for those users in my contacts list that are techies: after about 5 IMs, further chatting seems to organically migrate to a phone call or desktop client session (Slack/Volt/Skype/Discord) rather than the approx 3 messages every 5 minutes my cursory glance at message times in Signal shows for the non-techie users.