My FreeBSD Box's WEB serve sleeps?

[heccj]

My FreeBSD 5.3 Box have Apache MySQL and pureftp serve,and i start them
by adding
*****_enable="YES" in the /etc/rc.conf.
I meet an odd problem:
if the clients visit http serve via internet at the first time after a
long time(eg. one day),my box will delays for about serveral minutes,and
then it works very well.
But another box at the same situation that run with Windows server 's
IIS has not this problem.

thanks!