One thing I noticed when using this library: Instantiating the rtc object seems to hang the program for about 2 seconds. This didn't work for me in the project I'm working on because it needed to start processing input right away. I didn't trace down why it took so long. Is that normal to take 2 seconds?
If you give me a hint may I can help is it this part?
// Select the Slowclock source
or does it came from this line?
By the first part it happend about the external xtal to swing-in