Time permitting = if there is time available
"I'll come and spend a day with you in April, time permitting."
If there's time = we use this phrase if we wish to say that something will go ahead or proceed if there's adequate time.
"If there's time, we'll have a quick meal after the show."
Time permitting =時間があれば、
"I'll come and spend a day with you in April, time permitting."
If there's time = 充分な時間があれば、何かが先に進んだりできたりだろうことを伝える時に使います。
"If there's time, we'll have a quick meal after the show."
もし時間があればショーの後にご飯を食べるよ。
1." I'll stop over once time permits."
"Once time permits" is a phrase which means "once time is available" or "once I have the time."
2. "Once I have the time, I'll stop by."
This is a direct and simple statement.
1." I'll stop over once time permits."
（時間が許せば立ち寄ります。）
"Once time permits"（時間が許せば）という言い回しは、
”once time is available"（一度時間があいてれば）
"once I have the time." （一度時間があれば）
という意味のフレーズです。
2. "Once I have the time, I'll stop by."
（いったん時間があれば、私は立ち寄るよ）
これは直接的で簡単な言い方です。
examples
"I'll pop my head in when I'm near you and say hi".
a casual way of saying i will visit you when I have some time.
or
"I will drop by when I'm in town".
or
"When I get time I will pop in and see you, have a catch up".
a catch up is a way of saying have a
chat but more informally.
"I'll pop my head in when I'm near you and say hi"
近くに来たらちょっと顔出すね。
時間があるときに行くねというカジュアルな表現です。
"I will drop by when I'm in town"
街に行ったら寄るね。
"When I get time I will pop in and see you, have a catch up"
時間があるとき、ちょっと寄ってしゃべりにいくね。
a catch upとは、おしゃべりをするというカジュアルな表現です。
You could just say "I'll try to stop by", "I'll try to pop in" or "I'll try to make it", however, as you are busy that day/evening and you may not have the time, its nice to add this on the end. Otherwise, the person may be wondering why you did not come. By adding 'If I have the time' on the end, it helps the person understand why you couldn't come if you don't have time to go.
この場合、"I'll try to stop by"、 "I'll try to pop in" 、 "I'll try to make it"ということができます。しかし、忙しくて時間がないかもしれないときに、最後にこう付け加えるといいでしょう。 そうしないと、その人はどうしてこなかったのか気になるかもしれません。
'If I have the time' と最後に付けることで、もし時間がなかったら行くことができないとわかってくれるでしょう。
When you are asked to go somewhere, but you are busy or not sure you will be able to make it, you will say something along the lines of " If I have some free time" or "If I have the time to do so". If you only have to be there quickly, you could say "I'll stop by for a few minutes". Above I have given you two ways to say how you will stop by if you have the time.
Thank you for your question!
I will stop by ____________ later if I have the time.
if you would like to express to someone that you will stop by somewhere if you have the time, you can say something like "If I have some extra time later I will stop by _______." or "I'll stop by ________ should I have some spare time later.". By using the words "spare" and "extra", this shows that you will only stop by wherever it may be if you have more time left after you have done something else before that or errands.
This is a very simple sentence that can be used to let somebody know that you will see them when you can. You may be very busy at the moment, and don't know when you will be free.
By saying "if I have time" you are letting the other person know that it is not a guaranteed thing that you will indeed be able to see them or a place.
1. I'll make a quick turn if I have time to spare.
To make a quick turn means to visit someone quickly.
Time to spare means if you have some time left after
completing your errands, chores, meetings, etc.
Example: When he had time to spare, he made a quick turn
at his grandmother's house to drop off some flowers for her.
2. I'll pop in if time allows.
To pop in also means to visit for a short while. If time allows
refers to having time to spare to make the visit.
Example: If time allows after the movie, we can grab a quick
pizza before heading home.
Depending on if I have time, I will stop by for a bit.
Here are some examples of these dialogues being used in context. I have a lot to see on my road trip, but I will pop in to visit if I have time. I have had such a busy week. Depending if I have time, I will stop by for a bit.
日本 
イギリス 
カナダ 
南アフリカ 
アメリカ合衆国 
アイルランド 
ニュージーランド 
