That apparently makes very little difference. I listened to an interview with a Yale professor who cited stories that showed minimal impact. The supposed reason is that by the time you know a country has an outbreak, it's already to late and people from there will have travelled to your country. What apparently had been shown to be very effective is preemptive school closures. Unfortunately that's a tough call because we can't have a well functioning social system liked other developed countries.

Interview: https://samharris.org/podcasts/190-respond-coronavirus