Ancestry DNA Tests - Samples and Resamples

I've read and seen in various forums the suggestion a person should give their Ancestry DNA sample (saliva) first thing after waking up.  The reasoning being there should be the maximum number of cells, formally part of the tissue of the inside of the mouth, suspended in the saliva.  This made sense to me until a met a person who followed this approach - twice - and had her sample rejected twice.  Upon inquiry with Ancestry, she learned this 'first thing after waking' approach can present too much bacteria in the saliva.  Yes, that makes sense too.  The suggestion from Ancestry was to eat a meal, wait 30 minutes or so, and then give the sample.