I have explained about this problem via video please see the video here:
Strange Problem About Youtube API
I am having a strange problem about youtube API . For example
http://gdata.youtube.com/feeds/api/users/tryingtobesikh
the above api return with the subscribers count. But when someone subscribe , it doesnt update instantly after refresh. But the strange thing is , it updates when i press f5(refresh) two times at once. Don't know what is the problem, may be some cache prob? I am working on a script where i need to check if someone subscribed or not intantly. If the user subscribed do this , if didn't do something else. So i need instant subscribers count changes. Any type of help will be really appreciated.
The official YouTube API documentation does note that there may be delays with data updating: http://code.google.com/apis/youtube/2.0/reference.html#Overview:
Statistics, such as the number of times a video has been viewed or the number of comments available for a video, are typically updated within 30 minutes to two hours after the upload completes. However, this delay may be longer under heavy API server loads.
On an ongoing basis, statistics for a video are typically updated every 30 minutes to two hours. However, updates may occur less frequently under heavy server loads or for videos that are viewed very infrequently. In search feeds, updates to ratings and view counts could take as long as a couple of weeks for infrequently viewed videos.
On a side note; I've only used the YouTube API once myself, but seen as you said you need to check if a user has subscribed to another user, maybe you could try looking into the activity feed API? as this contains information about recent subscriptions:
https://developers.google.com/youtube/2.0/developers_guide_protocol_activity_feeds