Have you heard from George recently? I’ve met a lot of people in the last few days. Everything is going well. We haven’t had any problems so far. I’m hungry. I haven’t eaten anything since breakfast (=from breakfast until now). It’s nice to see you again. We haven’t seen each other for a long time.
We use present perfect with today/this morning/this evening etc. when these period are not finished at the time of speaking.
I’ve drunk four cups of coffee today. (perhaps I’ll drink more before today is finished) have you had a holiday this year (yet)? I haven’t seen Tom this morning. Have you? Ron hasn’t worked very hard this term.
Note that we say ‘It’s the first time something has happened.