Depends how long it takes for you, some people need longer than others (and if also differs per insulin - some do work faster than others)
Are you going low before eating or very shortly after eating - if so then yes it could be a bit early
Can also depend on time of day, before I got my pump I used to have to pre-bolus by a good 30 mins before breakfast, but only by 5-10 mins before lunch/dinner
Good morning. My DN thinks I'm bolusing too early because of guidelines. I have gone back to what I've been doing 30mins before which works for me. I have just been put on new long term and still doing a bit of tweaking. I have a libre which is a great help