When is the best time to have an ultrasound done to confirm pregnancy?

Don't bother, unless you absolutely must know whether she's pregnant or not.   And always remember even if she's scanned and confirmed pregnant, that does NOT mean she will carry to term necessarily.   She may, or may not, be pregnant at the time of the scan.   IF I'd bothered to have this done, I'd still have been watching around a due date, in case the scanning was inaccurate.

Minimum 28 days, 32 days ideal.

Thank you

I’ve had my [small breed] scanned at 30 day’s, showed one empty sac, scanner said she had re absorbed. I’ve read on here this is common, today she seems swollen slightly around her nipples, scanner also said could be phantom pregnancy I didn’t expect a empty sac with phantom just the signs. Has this happened to anyone, when would you recommend a re scan, thanks in advance. Lucy xx  if she’s not having pups how long to the empty sac goes, yesterday she was licking herself having a little cry, otherwise seems fine xx