bacteria attain mutations onlymost propably under stress mainly though plasmid transfer ... This is the most common way that a mutation or alteration of character can occur over a short period of time...

The best way to be exta sue , make glycerol stock and preserve at -80

good luck

if media did not became dry . it has moisture , you can use , I think. it did not feel any nutrition suppression. Chance of mutation is very less.

Up to 3 weeks should be fine. You should culture them right away. Here is an article for reference:

Genomic Changes Arising in Long-Term Stab Cultures of Escherichia coli

doi:10.1128/JB.186.19.6437-6442.2004

Thank you so much for all your answers