Method to set the default value for current timestamp

You can use useCurrent() method for your custom timestamp column to store the current timestamp as a default value.

Schema::create('posts', function (Blueprint $table) {
    $table->id();
    $table->string('title');
    $table->timestamp('added_at')->useCurrent();
    $table->timestamps();
});

Tip given by @iamgurmandeep