Heart rate Monitoring

Yes, just open the Health app on your iPhone and tap on the appropriate tab for the timespan you want to see. You have the choice of hour, day, week, month, or year and you can drag the plot to show any date and time you wish.

You can also see current day in the heart rate app, just open the app and tap on Current, and it shows a tiny graph. It is too small to show much detail, but it should get you started.