How do I let someone know of my available times to meet?

Sounds like you've worked this out for yourself.

Whenever you give someone a time to meet, give them only the times you are available that allow you to make your next appointment. If you need to end by 2pm to make sure you are at your 3pm appointment, say so.

Most, reasonable, people would not consider you rude to state exactly when you are available. After all, this is considerate to them too so you don't run out on them mid-sentence.

12-3 pm isn't appropriate for any meeting coz that's lunch time for everyone...unless you have an earlier lunch, say from 11am-12pm...the best thing to do is explain briefly your busy schedule to your partner to avoid being misunderstood...just tell her why you can't have lunch at such time...be available for her when you are available...12-2pm would be a good time to have a lunch with her...rest for an hour before you go for your meeting...after meeting, you can go for a cuppa coffee unless your meeting drags up to dinner time...

tell your friend that ya'll can meet between 12:00 and 2:00 for lunch, because you have to be @ a meeting @ 3:00. That way, the friend will know exactly what time frame you mean

say you can meet at 12 - leave it at that.. then when it gets close to the time of your meeting, let her know you have to go... this way you don't seem to have her 'scheduled', you know?