how to code irregular time periods??

i have the following data:

a = xlsread('outdoorall.xlsx','G2:H52364');

b=xlsread('indoorall.xlsx','G2:H52364'); %2397

time=xlsread('outdoorall.xlsx','G2:G52364');

for i=1:2364

dt=(b(i+1)-b(i)); % change in indoor temperature divided by time

c=dt/a(i)-b(i);

plot(c)

end

the problem is my time periods are irregular so im struggling to code DT above as idk how to set time??? i dont want to use xlsread due to this

i was told to find a function or code it by myself but idk understand matlab very well

also is my for loop correct??