Bluetooth is not an instant transmission protocol and there are some lag / delay due to the time it takes for the signals to be encoded and transmitted. Typically if you're listening to music or audio only, you won't ever notice this lag.
However, pair audio with video or use Bluetooth devices with musical instruments where the user expects instant feedback and it is noticeable.
In general, the lag should be between 0.2 to 0.5 seconds. But there are some factors that can increase the amount of lag / delay you experienced.
If you wanna enjoy lag-free content streaming with Bluetooth transmitter, please kindly notice that Low Latency supported Bluetooth headphone or speaker is required, even both supported, there might be a latency of 40ms.