Safety relay toggle time
I assume you mean how long will it take the relay to open and interrupt power to its load.  I'm not sure if that 300/minute spec holds the answer to the question, but it does suggest an upper limit of maybe 100 ms.  In practice it depends quite a bit on what kind of coil suppression is used.  For more info see: http://www.cbxelectronics.com/pdf/app-notes/app-note1.pdf