Is this a bug or a feature? Friend help menu

I'm not sure if this is a bug or a feature... but sometimes when I click the "speedup" button on a construction task it doesn't show me the option to ask a friend.  It still shows all the other options to use books.  I can't find a pattern to it, but maybe there is some sort of timeout going on?  Has anyone else noticed this?

I'm not sure if this is a bug or a feature... but sometimes when I click the "speedup" button on a construction task it doesn't show me the option to ask a friend.  It still shows all the other options to use books.  I can't find a pattern to it, but maybe there is some sort of timeout going on?  Has anyone else noticed this?

You can only ask every 30 minutes.

You can ask help from friends to speed up a construction only if its building time is over 15 minutes.

Ah, that makes sense.  Thanks.