Hypothesis: your friends are not too far away from your peer group(?). They share similar hobbies, structures of their days, social environments and occupations.
If they don’t make a conscious effort to answer in a specific time frame it’s just natural behaviour that you respond in similar times.
I haven’t seen this thread. I read only the top comment, then wrote mine.
If you know you have npd you are about 2000 times better than most people who have it, as you have said it’s not a good thing to be diagnosed with it and yet you acknowledge that you have it. That’s like you are able to acknowledge that you are not unfailable or perfect.
If you really care about your friends and family you should look into therapy.
If you are interested in NPD you could really read up on the topic. If you want to know if you have npd symptoms I would suggest to ask people who you trust and who know you well. Ask them, then listen carefully, and if 3 independent people tell you what they think of you, believe them.
Do not ask them suggestive questions, but try to ask fields or topics that npd people can have symptoms or indicators in.
As others have written it’s deconstructive towards other people plus NPD are hard to make understand their behaviour is problematic. In their view you are the problem if you have a problem with them. Depression, ADHD and other things do not have that trait. With them you can talk them into therapy and about potential problems they are causing.