When you build the Flutter app the first time, it will take a longer time. It is because the Flutter built the device-specific APK or IPA file. Thus, the Gradle and Xcode are used to build the file, taking a long time.

The first Flutter app build may take longer than subsequent builds due to several reasons:

Downloading Dependencies: Flutter needs to download and cache dependencies when you create a new project or run it for the first time. This includes the Flutter framework itself, as well as any additional packages or plugins your app relies on.
Building the Dart to Native Code: Flutter apps are written in Dart and compiled to native code for the target platform (iOS or Android). The initial build involves converting Dart code to native machine code, which can take longer than subsequent builds since subsequent builds may only update the changes.
Setting Up Gradle and Other Configuration: If you are building an Android app, there might be additional setup tasks that need to be done, such as configuring Gradle and setting up the Android project.
Initializing the Project Structure: Creating a new Flutter project involves setting up the project structure, creating necessary files, and initializing the project with default configurations.

Subsequent builds, especially during development, are typically faster because Flutter can utilize its hot reload feature, updating only the changed parts of the code and avoiding a full rebuild.

If the build time remains consistently slow, you may want to check your project for any large assets, unnecessary dependencies, or complex code that could be optimized. Additionally, upgrading Flutter and Dart to the latest versions may include performance improvements.