If you get sentenced to a day or two in jail, most courts will not grant work release, but will allow you to do it at a time that is relatively convenient for you. Often you can schedule the time in advance. It will be up to the jail if they will allow you to do it on a weekend, not all jails allow it.
In terms of work release, I find that most judges will authorize this in cases where the person is sentenced to more time in jail.
Depends on where you are and how long the sentence is. In Spokane, most judges will allow work release on cases where you must spend a week or more in custody. In addition, you must meet the work release requirements of the facility where you are doing your time.
If the time sentenced is a week or less, the judges may be willing to break up the time so that it is served on consecutive weekends, allowing you to do the time while not scheduled to work.
Work release will generally require a pre-interview with the corrections department. If you or your lawyer are able to negotiate it, participation may require a longer period than if the plea were to straight time.
Depending on the sentencing court, any jail time you must serve may be done according to your own schedule. Many times, you can even pick the jail where you want to serve your time. Again, though, this all depends on the judge who sentences you.