Question with EEG and PPG bluetooth data parsing.

[XlashDev]

Hello! I am making an android app to stream both EEG and PPG at the same time via bluetooth and currently I use the time stamp included in the bluetooth characteristic value and one data from the sample to display in my current graph.

I only used EEG for the meantime. (1) My question is how do you create timestamp for the multiple data receive when only one timestamp is included on the 20bytes characteristic.?
e.g.

data receive[0] ----- timestamp?
.
.
.
datareceive[11] ---- time stamp?

(2) What channel do you utilize in PPG ? If I understand the code right it is sequentially sent. Utilizing all 3 channels?
(3) same with question 1 - but timestamp for multiple PPG?
(4) Im getting negative value from eeg data. What I did , first 16bit timestamp then succeeding 12bit converted to int with rightmost digit as starting point and so on. Is that right? e.g. 3A FD FC DE FA.... (3AFD-timestamp) (sample one FCD) (sample 2 EFA) and so on?

TIA