like i'd be talking to them via text or facebook, or even in person. and i manage to say something like

"hey well im going to this place, you should come with" and they agree. but when the day comes, the seem to flake. it happens so frequent its frustrating.

here are my recent examples.

me: hey you wanna go play darts? i know this cool place we can check out
her: okay sure. sounds good. what time?
me: around 7pm.
*6:30pm comes around*
her: hey my girlfriend just invited me to eat with her. we can hang out another time

example #2

me: hey i'm heading out to starbucks later on, in about 2 hours, why don't you come along?
her: okay
*when its time to get picked up*
her: hey sorry, i have to go baby sit


------------------

would it be better if i ask them to do something like 4-5 days prior?!

You don't give context on how you met, but:

a) women you meet in clubs, you meet them when they are horny and drunk, the day after they are not in the same mood and feel regret, unless you spent a lot of time talking or they really felt for you (rare)

b) You're too cold. You have to express a will to be with them. Not to play darts "and if they want they can come". I would feel like an accessory. Express your intention to KNOW HER, not to hang out for lame activities (or not lame) she does not care about. If she's interested, she's interested in knowing you, not playing darts.

just my 2 cents.