quark2-
I touched on this earlier – is it a stirah in rashi, from 25: were ksus lailah goes by time, and elsewhere, where ksus lailah goes by the beged?
Regarding your query. You wrote:
this would mean, that is someone had the (strange) minhag to wear pajamas during the day, that would be considered ksus yoim for him (although it is possible that this would only be true if the beged was made specifically for him)