Nine times out of ten, the UDRP recipient is not going to know the commencement date, or they are going to be confused by the flurry of things they have received. For example, the first time that many people become aware of a pending dispute over their domain name at the NAF is when they are copied on an NAF notice to the complainant pointing out deficiencies in the complaint as filed (and as not served on the respondent).
In that situation, you will have to contact the NAF if you want to get an advance copy of the complaint which *should* have been served on the respondent. In the same situation, WIPO will then ask the complainant to send it, but you will find that some complainants will *still* refuse to provide a copy:
Of those, the respondent is more often than not confused about what they have received, and will believe that the five-day correction deadline set in the notice is, in fact, the UDRP response deadline.
The only sane way to avoid gross malpractice here is to get an identification of the dispute resolution provider and to contact the case manager for the particular dispute. I am not aware of any attorney who regularly represents domain registrants who does not check the deadline with the provider. It also is quite helpful to nail down what time zone the respondent is in, since that also determines what "day" it is there (as counted by the provider per the other thread here).