I have a couple of questions regarding Notifications and how the works

I have an algorithm, running at hourly timeframe, that trades  lots of stocks

I implemented notifications in order to get alerted when stocks are opened and closed

During peak time, I could get  more than 20 messages sent from the algorithm.

To stay within the max number of  calls per hour( 20 ) limitation I put messages in a “queue” in order to  postpone message sendings to the following hour

Here' s the first question:

 it seems that when a high number of messages ( more than 20) at hour x is generated,   the following hour get “skipped” in the sense that   at hour x+1 exceeding messages (from 20 onwards)  are not sent and get “lost”.

 My suspect  is that due to the time needed to sent the first 20 messages ( let's say that the latest message takes 10 seconds to be sent) a full hour is not yet completed when I start sending the remaining messages. message are triggered but in reality are not sent

could anyone confirm that?

My second question is : 

the limit of 20 messages is “per channel”( web, mail sms) or is per generic notification ( 20 in total cumulating all the message sent on various channels?) thanks