Only when the exchange is open :)

Depends on the pre-market price. If the stock is not volatile, it is fine even when the stock market is closed.

As long as the price is good and I know that 99% of the time there is no risk of anything bad, I don't have a problem with placing an order at night to buy the next day. Otherwise, definitely not.. 🙂

Personally, only when the stock market is open, I like to set some kind of limit and when the stock reaches it that day or that week, I buy. I think of the weekend as Poles Sunday. Everything is closed so no buying. :D