2 emergency room visits on same day

Yes, we do it all the time. If the patient is discharged home and come back for the same reason you can still bill with the same dx, you may need to add mod 27 if billing for the facility.
I would also send the documentation of the times for example, 9:30 am, 5:00 pm
Modifier 27 is for multiple outpatient hospital E/M encounters on the same date. This is only used for the hospital and is never to be reported by a physician.
two E.R visits the same day

For professional charges are modifiers needed when two E.R visits are performed same day (25)
The professional services modiifer(s) are -76 if same ED provider see the patient, if different ED provider then modifier -77 is used.

Patient in the ER for two days before being admitted to inpatient. Can more than one doc charge an ER visit? What would be the code for the first and second day?
LABS on each of the visits

Hi a subsequent question to the two ED visits scenario

Identical labs were performed during both visits. which modifier is appropriate?
59. 76 or 91?

Thank you in advance for your time.