You type /dayspeed and then a number value. Try starting with /dayspeed 1000 and go up or down from there. /dayspeed 0 will stop it... I usually use 300 as the value. you can choose a specific time of day by doing /daytime followed by a 24-hour clock time. For example, /daytime 2330 would be 11:30 at night.

How can I make the daycycle extension on psyspades slower? Since it goes quite fast on my server at the moment.