She may be setting that time limit because she doesn’t want you to think that she is very into you.
It may be a way for her to protect herself or create a buffer to guard her heart.
She may have had a previous relationship that ended badly.
Perhaps she felt that she gave this person so much of her time only to have him hurt her or betray her in some way.
She becomes cautious as a result.
She may not want to put herself in that kind of situation or vulnerability again.
She sets time limits with you in response to that experience.
Again, she may simply be trying to protect herself in these instances.
She may not want to allow herself to get too deeply involved too early in your interaction with her.
She may want to set the tone for the meet ups that you have with her so that you don’t instantly believe that she is all over you and all into you.
The reason why she tends to stay longer after you meet up could be because she just loves your company and ends up not wanting the date or meet up to end.
She gives in to her desire to spend more time with you because she is truly enjoying being around you.
There may be a part of her that keeps wanting to stick with the time limit during the meet up but she is having a good time and this makes it difficult.
She may begin to get worried that she is acting like she did in her previous relationships.
She is beginning to give you too much of her time.
She may find herself beginning to develop feelings too soon.
She is worried.
So she decides that she will give you only a few more minutes.
However, those minutes become stretched out as she continues to enjoy your company.
After those extra minutes have passed, she decides to give you just a few more just so that you can finish that thought. However, those few minutes have now stretched to a half hour or more.
This is most likely a girl who is wrestling with her feelings.
On the one hand, she truly is enjoying her time spent with you and wants it to last longer than the time limit that she sets.
On the other hand, she is being really cautious and doesn’t want to appear as though she is overeager.
She may also tend to set these time limits because she is not quite sure if she wants to be in a romantic relationship at this time.
She may be single but is wondering if she truly wants to jeopardize her freedom.
As a result, she sets the time limits because she isn’t too keen on allowing a decent amount of her free time to be used up by being with you.
However, during the meet, she has such a great time that she figures that she can delay that shopping trip that she had planned for after the meet up with her girlfriend.
She may keep setting these time limits for a few more meet ups with you.
Ultimately, if she continues loving your company, she will loosen that time limit more and more until you notice that she isn’t putting a time limit at all.