How to custom MySQL ORDER BY

Is it possible to write custom ORDER BY statement in MySQL

I mean, I have database like this,

id  time  day

1   1:55  Mon
2   2:00  Sun
3   1:00  Mon
4   3:00  Tue
5   2:30  Sun

I can write order statement like this,

SELECT * FROM mytable ORDER BY day

but is it possible to write query to get Sun as first and Tue for second and Mon for third

This is wrong but like this query:

SELECT * FROM mytable ORDER BY Sun, Tue, Mon