Here's a spectogram of a speaker's rendition of “プロトタイプ” from English “prototype”, collected from Forvo
It should be clear from this spectogram that the pu-mora is pronounced in half a mora; the mora-length in this segment is about 0.16 ms and pu takes about 0.08 ms; the entire tai is also pronounced in about 1.5 moræ.
I've definitely encountered this multiple times in speech, and it wasn't hard to find examples on Forvo at all. I couldn't find any published research on the matter; is this normal? I've heard “ナイス” from English “nice” pronounced with nai as seemingly one mora, and it again wasn't hard to find examples of this on Forvo and confirm it with acoustic analysis.