My first time buying stocks using brokerage. Which time window should i be looking to buy within?

If your broker doens't allow pre/post market trading, setting orders outside of regular market hours is useless and the orders will activate when the market opens. The key risk here is that if you set the order before the market opens and the price changes drastically before market opens, you might get filled at a terrible price.

If your broker does allow pre/post market trading, generally, trading outside of regular market hours, the stock will see less volume, meaning that the bid-ask spread might be quite wide and you might find it hard to get your order filled/filling at a bad price. This is especially so for smaller or less popular stocks.

Other than that, trading pre/post is largely the same as trading during regular market hours.​​​