import datetime
ts = 661391999
dt = datetime.datetime.utcfromtimestamp(ts)
print(dt) # 1990-12-16 23:59:59const ts = 661391999;
const date = new Date(ts * 1000);
console.log(date.toISOString());
// 1990-12-16T23:59:59.000Zimport java.time.Instant;
import java.time.ZoneOffset;
long ts = 661391999L;
Instant instant = Instant.ofEpochSecond(ts);
System.out.println(instant);
// 1990-12-16T23:59:59.000Z