EDIT — Edited to produce only the data from the time criteria are met until the end of the data.
See if this does what you want:
D = load('mycolumns.mat');
Ix1 = find((D.acc < 10) & (D.C < 20));
t0 = D.time(Ix1(1)); % First Time Criteria Met
new_time = D.time(Ix1:end)-t0; % Time From ‘t0’ To End
new_acc = D.acc(Ix1:end); % Corresponding ‘acc’
new_C = D.C(Ix1:end); % Corresponding ‘C’
figure(1)
plot(new_time,new_acc, new_time,new_C)
grid
legend('acc', 'C', 'Location','NW')
xlabel('time')
