As long as you don't lose by running out of time than you can play at whatever speed you want. It might annoy your opponent that you aren't "blitzing" like they want you to, but that's about it. 

On the other hand, if you get the reputation of being a painfully slow player, eventually people will start avoiding playing with you. Most people here just play for fun, and don't agonize over every move. It's one thing to stop and think hard about a complicated tactical situation, and it's another thing to take 20-30 seconds for every single move. Typically, 5-10 seconds per move should be long enough. Longer than that, you are probably over-thinking. Try and develop a feel and a flow to your game that lets you play at a natural pace.