I was told by Dr. Laidlaw years ago that nurse bees feed larvae about every
15 minutes.  He suggested that combs of brood should be returned to the
hive in ten minutes, since it takes the bees some time to respond to the
brood.  Obviously, this would take care of the chilled or drying larvae
issue.
 
You can buy queen grafting tools from one of the major bee suppliers in the
U.S. and I presume in Canada.
 
Michael Palmer stores queens over an excluder.  I've seen that done
successfully several times.  I have even done it successfully in a top nuc,
over a parent colony with honey supers in June and July.
 
Regards,
 
James C. Bach
WSDA State Apiarist
Yakima WA
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