How to figure it out the correct way to find out accurate delay with my curtain car audio?

Hello
With my GLC 300, I have 3 way car audio system that contains a DSP and amplifier (rainbow- DSP amplifier L8.2), which have only 2 input options: 6-channel high level (connected to the Original audio car unit) and bluetooth (can connected directly from iphone or PC with Rew installed).

If I play sweep from REW to check delay from speakers, I can not get accurate delays due to bluetooth latency.
The only solution is I play the sweep file from USB on the car MBUX unit, and immediately click on Start button on REW. To minimize errors caused by pressing Play on the MBUX head unit and the Start button on REW not being perfectly synchronized, I want to measure each speaker 5 times and then average the results to calculate the delay. From the settings window in the Measure section, I selected ‘No time reference’ under Timing. Which of the following three options should I choose next: ‘Set t = 0 at Peak’, ‘Set t = 0 at Estimate Delay’, or ‘Set t = 0 at IR Start’?
Could you give instruction to get right delay of each speaker in this case?
Thanks

Easiest would be Measuring with file playback.

I got this, thank you so much for such very quick and nice response. I have another problem, would you give your comments?
- The factory head unit in my car has already been configured with delays, phase, and EQ to match the vehicle’s basic stock speaker system. The above solution can help me if I listen to music through the factory head unit.
However, in the case where I play music directly from my phone via Bluetooth connected directly to the DSP, I need a separate tuning setup. So, when playing a sweep in REW and sending it via Bluetooth to individual speakers, is there a way to accurately measure delays? I’m fine with measuring multiple times to average each speaker, I’m just not sure which method I should use.
I can use a ruler to measure the actual distance to each speaker and manually calculate the delays, which seems relatively reliable, but in case I want to use REW to measure them instead, is there any solution?
Thanks

The acoustic timing reference could be used to cope with any latency, but it might struggle in that highly reflective environment.