Date has the time as well, just add HH:mm:ss to the date format:
import java.text.SimpleDateFormat
def date = new Date()
def sdf = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss")
println sdf.format(date)
In case you are using JRE 8 you can use LoaclDateTime:
import java.time.*
LocalDateTime t = LocalDateTime.now();
return t as String