How much time does it take?

There's no fixed formula - it isn't a simple oral for 5minutes, finger her for 2 and stick it in...

Just let her get used to you, reassure her and she'll become used to the feel of you over time - and feel that she can explore her sexuality around you more openly. If it's something casual use your hands, focus on the rest of her and don't pressure her. Remember women are all different sizes and have had different boyfriends in the past.

Try to see her telling you to stop as a chance to better pleasure the rest of her - instead of something stopping your fun - and you'll have a lot more fun yourself, too;)