When should I launch my app and how do I promote it to my attendees?

Launching The App
Because the app is live as soon as you start building it, “launching” your event information happens the second you start promoting it to your attendees. The earlier you launch, the more time attendees have to get the app, familiarize themselves with it, create their profiles, and begin networking, which leads to higher overall usage and a better ROI.

Having said that, you should develop the app enough that, when they access it, they are engaged and interested. If you want to launch the app but haven’t finished creating it, you can create a “Coming Soon” landing page.

Promoting The App
When you're ready to launch you will just need to communicate the Event URL associated to your event. The format of this URL will appear as eventmobi.com/eventcode, and will act in directing attendees to the Event Space. Alternatively, you can promote the EventMobi Universal App and your unique Event Code to have attendees access your event information from the app stores. 
Putting It In The App Store?
If a Custom Branded App is part of your package, then your app will be made available in the Apple App Store and Google Play. The timeline to submit, and have the app approved is 4-8 weeks, so you will want to make sure that you are considering this timeline into your anticipated launch date.