You do not need the loop.
Just do this:
timestr = ["758" "808" "828" "838" "848" "858" "908"]
timenum = str2double(timestr)
Note that times (link) is actually a MATLAB function for doing element-wise multiplication. Naming variables to be the same as MATLAB functions is called ‘overshadowing’. The times function will not do what you intend if you call it after overshadowing it, so I changed your vector names to avoid that.
