What a great question. Local business citations are extremely important in the eyes of google. Citations are considered mentions and if other people, websites mention your business using NAP (Name, Address, and Phone) this is a positive indicator that your are “real” .
You always want to do your citations after you have created your Google My Business page as google has a tendency to change address slightly. Once you have an approved Google My Business Page, you can start building citations with the same address Google has used.
Citations can take upto a couple weeks to become approved after you submit them. Adding up to 100 citations over a few days will no cause or create any problems.
We create business citations daily for our clients and have never seen any issues.