Installation date is natively collected by Batch's SDK. It means you can use it to create user's segments as "users who installed the app 2 days ago".
In the targeting block of your campaign, click on "Add conditions". Pick "Installation date".
According to your campaign's goal, set the number of days after installation ("Installation occured 2 days ago" in this example).
The advantage of these welcome campaigns is that you only have to set them once. Then, you can let them run in the background.
In the "When" section of your campaign's creation form, choose the "recurring" option.
Choose a starting and ending date for the campaign.
The notification needs to be sent everyday ( = every 1 day in the form) so all new users can receive their welcoming campaigns.
You're all set! Don't hesitate to reach out through the live support if you have any questions.