The shortest unit of time in mushclient timer is second.
If i want to get a time delay of one millisecond, what shout i do? Sometimes one second is too long for me.
When timers were designed it seemed unnecessary to allow for sub-second intervals. For on thing, Internet "lag" is often almost a second. For instance, I recently "pinged" www.smaug.org (Realms of Despair MUD), which took an average of 300 ms (almost 1/3 of a second). Then there is the time the server will take to process a command, say another half-second if you are lucky. So if Internet time and processing time, per command, are going to be in the order of a second, it seems pointless to allow you to fine-tune your timers to 1/1000 of a second. You may have increased precision, but not increased accuracy.
However, having said that, in MUSHclient you can set up a "speedwalk" delay in increments of milliseconds. So, if you need to speedwalk from A to B (or B to A), you can have each command issued every 100 ms if you want to.
In scripting (or in triggers) you can put commands into the speedwalk queue, so it is possible to issue commands therefore in sub-second intervals.