I'm not sure how long a remark will take, but IMO its almost always worth going for a remark if you are just 1 mark off the next grade. Remarks can often shift your final mark up (or down) by 1-2. If you lose 2 marks it won't be a big deal, but even gaining 1 mark gives you a higher grade. Even if it doesn't help you meet a university offer, a higher grade will still look better whenever a potential employer asks for your A-level grades.