I'm not sure what the rest of your dataset looks like unless you are looking to do a histogram of 7 points. However this snippet of code should help get you on the right track of extracting out the values.
%This section is only used to gen dummy struct.
daysofweek={'Mon','Tue','Wed','Thurs','Fri','Sat','Sun'};
for ind = 1:numel(daysofweek)
eval(['Weekday.MeanDistance.' daysofweek{ind} '=randi(10e3);'])
end
%exctact items from scrut into categorical.
for ind = 1:numel(daysofweek)
MeanDistance(ind) = getfield(Weekday.MeanDistance,daysofweek{ind});
end
hist(MeanDistance)
If you have more data for each week you can then change MeanDistance into a MxN array through additional indexing through the structure. By going through and extracting out the data into an MxN array and knowing each column/row (depending on how you'll be storing the data you can then perform the histogram in either direction and then relabel the axes to be string or number.