Problem in converting dates while plotting

I want to 3plot a xls file with scatter command. the format dates I have is like 2016.03.01 14:39:00. I used this code :

date=txt(:,1); %dates are in the first column
x=date(2:end); %plot dates beginning from the second cell
time=datenum(x);
Figure
scatter(time,num(:,1),12,num(:,10)),colorbar;
datetick('x','yy/mm/dd HH:MM:SS','keeplimits','keepticks')

The conversion gave me the same result for all the dates : 737061,697916667

Could someone help me ?

[dpb]

Use readtable and datetime instead of obsolete datenum