[時「とき」] => At the time A N5
Time
Vた[時「とき」] => After having done something N5
Time
[一方「いっぽう」]だ => Change A continues, A does not stop N2
Miscellaneous
[一方「いっぽう」] => On one hand A, on the other, B; Although A, at the same time, B N2
Contrast,Surprise