How to detect Android Bluetooth connectGatt() auto-connect completion

(*** Edit #2: Trying to connect multiple devices ***)

I am using BluetoothDevice.connectGatt() with auto-connect set to true to connect to multiple devices:

bluetoothDevice1.connectGatt(context, true, BLGattCallback(context), BluetoothDevice.TRANSPORT_LE)
bluetoothDevice2.connectGatt(context, true, BLGattCallback(context), BluetoothDevice.TRANSPORT_LE)

(*** Edit # 1 ***) I use onConnectionStateChange() in BluetoothGattCallback():

internal class BLGattCallback(val context: BTLeashService) : BluetoothGattCallback()        // Todo: Convert to LiveData
{
    override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int)
    {
        super.onConnectionStateChange(gatt, status, newState)

        val connectionStateChange = BLBluetoothManager.ConnectionStateChange(gatt, status, newState)
        BLBluetoothManager.connectionStateChange.postValue(connectionStateChange)
    }

(End Edit #1)

With this method I have to use a delay before executing my next connectGat() or else the previous one gets aborted. Why is this? I thought that it was not supposed to wait and just give a call back whenever it connects...

Is there a callback to let you know when the first connectGatt is complete so that I don't need an ad hock delay?

*** Edit #3 ***

By "first connectGatt is complete" I don't mean that a connection was made, only that I can now execute my next command without aborting the previous.

(End Edit #3)