they come out mostly at night.
oddish you have to get him at night time
yes, morning, day and night will be in HG/SS
route 30 night only
anywhere in kanto at night
forest at night
Bellsprout tower at night time.
Yes, in Safari Zone at night. And in Route 16 and 7 also at night.
go to the sprout tower in the town where you get the first badge at night.
It is found in Routes 7 and 16 at night and in the Safari Zone.
Level it up at night whilst it has high happiness.
unlocks night skys edge on the pokewalker