Twin B would not notice that time had slowed at all. To him, if he looked out a window, it would seem like the universe was moving past him, and therefore slower (remember, to him, he's at rest). So time is relative.
t w ɪ n WORD_BOUNDARY b iː WORD_BOUNDARY w ʊ d WORD_BOUNDARY n ɑ t WORD_BOUNDARY n oʊ t ɪ s WORD_BOUNDARY ð æ t WORD_BOUNDARY t aɪ m WORD_BOUNDARY h æ d WORD_BOUNDARY s l oʊ d WORD_BOUNDARY æ t WORD_BOUNDARY ɔ l WORD_BOUNDARY t ə WORD_BOUNDARY h ɪ m WORD_BOUNDARY ɪ f WORD_BOUNDARY h iː WORD_BOUNDARY l ʊ k t WORD_BOUNDARY aʊ t WORD_BOUNDARY ʌ WORD_BOUNDARY w ɪ n d oʊ WORD_BOUNDARY ɪ t WORD_BOUNDARY w ʊ d WORD_BOUNDARY s iː m WORD_BOUNDARY l aɪ k WORD_BOUNDARY ð ə WORD_BOUNDARY j uː n ɪ v ɜː s WORD_BOUNDARY w ʌ z WORD_BOUNDARY m uː v ɪ ŋ WORD_BOUNDARY p æ s t WORD_BOUNDARY h ɪ m WORD_BOUNDARY æ n d WORD_BOUNDARY ð ɛ ɹ f ɔ ɹ WORD_BOUNDARY s l oʊ ə ɹ WORD_BOUNDARY ɹ ɪ m ɛ m b ə ɹ WORD_BOUNDARY t ə WORD_BOUNDARY h ɪ m WORD_BOUNDARY h iː z WORD_BOUNDARY æ t WORD_BOUNDARY ɹ ɛ s t WORD_BOUNDARY s oʊ WORD_BOUNDARY t aɪ m WORD_BOUNDARY ɪ z WORD_BOUNDARY ɹ ɛ l ə t ɪ v WORD_BOUNDARY