I respond to e-mails 2-4 times a day during task transitions. The sender does not anticipate an immediate response so the 1-2 hours delay is OK.
Compare this to Slack which requires constant monitoring where senders anticipate an immediate response. Not to mention the increase in casual "water cooler" conversations.
The find the same people that recommend Slack are the same people that recommend 3-hour meetings. It's procrastination veiled as productivity.
Water cooler conversations are a kind of stress dissipation response for some people. It's great for some, bad for others. Slack means that it stays in a channel instead of at the water cooler when all you want is a drink, not a chat.
The only exception are meetings and escalations when something is on fire.
The first few weeks before and after a major go live, especially if there is new functionality, management will expect their team leads/single responsible individuals to respond immediately. Even if they don’t say it. The CxO’s, sales, and implementations folks will send you an email then immediately send you a Teams message asking you did you get the email and if they don’t hear from you, call you on Teams.
On the other hand, most days if it isn’t a major client issue, it’s mostly like you said, there isn’t a real expectation of an immediate response.