There are three main issues here: you are printing the literal string 'time' to the file, instead of the contents of the time variable. The second issue is that you should use the fileID as input to fclose. The third issue is that you didn't specify the write permission in fopen, so it didn't generate a valid identifier.
Also, you don't need close all here, nor clear all. The later should never be used anyway. In a debugging context you can consider using clearvars instead.
The code below should do what you need.
time = datestr(clock,'YYYY/mm/dd HH:MM:SS:FFF');
fileID = fopen('trialt.txt','wt');