Perplexing sentences

1. ...........seeing the snake, I ran away.

a) On b) When c) While

2. I used to arrive.......my office on time.

a) at b) in c) to

My answer :

1. a

Is it true that 'when+ inf. + -ing' is used to express a habitual action in the past?

2. at

Is 'to' OK, too?