Oanhle probably answered your question about the "pace" and the length of sounds when she gave you the list of the vowels diphtongues and triphtongues in Vietnamese at this link http://www.italki.com/question/253752 As you can see, a word can stretch a lot. For instance, nguyễn (like the name) will sound slightly longer than học (study). In fact, the words ending with the final stop consonants "t", "p", "c", "ch" are pronounced very quickly because, as the name says it, there is no air expiration after them, you "stop". That is unlike in English where you still let air go after pronouncing a final consonant. Such words only take two tones, a high tone (as in thất, to look) and a low tone, (as in học, to study). You just say the word with a high pitch or a low pitch, no rising nor declining. While listening to audio, sometimes I confuse two short words for a long one, so it is correct to observe that the length seems different. Hope that helps!

Valeuraph must have studied hard :)). I just want to add some information. Vietnamese words have no stress like English. You just follow 6 tones in this below link. And when you say a sentence, you also raise your voice at some words such as what (cái gì), where (ở đâu), who (ai), not (không) like English.