Actually uCoz offer an alternative to do this, but You have to go first to the module settings and active the option that says:
Enable the option to choose a post's publication date:
Necessary for adding entries with specific dates that are not the current date.
and also tick the option Do not display entries dated later than the current date
After active those options you'll be able to select the date of the post, article, etc so for example you can write the post today and set the date of tomorrow morning so uCoz will keep hidden the post until that date and time.
So basically you can write the post and schedule it by selecting the date in advance.
And remember that in each module you have to set the option first in order to be able to select a date in advance.
I hope this help... (also keep in mind the server uses his own time zone so you have to check it on the control panel and select the proper time zone according to your region).
I recommend to allow the uses of this feature (select date of the post) only to admins or moderators otherwise standard users will be allowed to change the date of any material so keep an eye on who can add/edit post on your website and set the permission accordingly under the permission setting of the users module.
This is not an automatic posting option because you have to write the post first but is an alternative