use commit time as mtime for file archives.
now output from two run of "hg archive -t zip" is same.
#!/bin/sh
mkdir t
cd t
hg init
echo This is file a1 > a
hg add a
hg commit -m "commit #0" -d "1000000 0"
echo This is file b1 > b
hg add b
hg commit -m "commit #1" -d "1000000 0"
rm b
hg update 0
echo This is file b2 > b
hg add b
hg commit -m "commit #2" -d "1000000 0"
cd ..; /bin/rm -rf t
mkdir t
cd t
hg init
echo This is file a1 > a
hg add a
hg commit -m "commit #0" -d "1000000 0"
echo This is file b1 > b
hg add b
hg commit -m "commit #1" -d "1000000 0"
rm b
hg update 0
echo This is file b2 > b
hg commit -A -m "commit #2" -d "1000000 0"
cd ..; /bin/rm -rf t
mkdir t
cd t
hg init
echo This is file a1 > a
hg add a
hg commit -m "commit #0" -d "1000000 0"
echo This is file b1 > b
hg add b
hg commit -m "commit #1" -d "1000000 0"
rm b
hg remove b
hg update 0
echo This is file b2 > b
hg commit -A -m "commit #2" -d "1000000 0"
cd ..; /bin/rm -rf t