plotting a variable x axis

Hello!

I have a timeseries that I was plotting with standard x and y axis. I just spoke with my PI though and she would like me to plot the x-axis vs. timeseries in time chunks.

I have two questions:

1) the math isn't coming out right; the x axis comes out to around 360

2) is what i am doing actually going to parse my data correctly?

i.e. the first 12 images are spaced 15 s apart, the next 8 spaced 30 s apart, etc.

%% changing x axi

whole_ts_pet_1 = [1:12]  
whole_ts_pet_2 = [13:20]
whole_ts_pet_3 = [21:53]
whole_ts_pet_4 = [54:63]
whole_ts_pet_5 = [64:68]
whole_ts_pet_6 = [69:71]

ttt_pet_1 = (whole_ts_pet_1*15)/60   % 3 min
ttt_pet_2 = (whole_ts_pet_2*30)/60  % 4 min
ttt_pet_3 = (whole_ts_pet_3*60)/60 % 33 minutes  
ttt_pet_4 = (whole_ts_pet_4*120)/60 %30 min
ttt_pet_5 = (whole_ts_pet_5*180)/60 %15 min
ttt_pet_6 = (whole_ts_pet_6*300)/60 %15 minutes

%% 

ttt_all = [ttt_pet_1, ttt_pet_2, ttt_pet_3, ttt_pet_4, ttt_pet_5, ttt_pet_6]

figure;
ax1 = subplot(2,1,1)
hold on

hold on
plot (ttt_all, d_tac_ts_2); hold on 
plot (ttt_all, d_tac_ref_ts_2); hold on