"Schedule in advance" vs "schedule". Is "in advance" unnecessary?

Solution 1:

While "schedule in advance" would seem on the face of it to be redundant, it's a frequently-used phrase and is meaningful in the sense of setting the schedule or obtaining the reservations or whatever some significant period of time in advance (days/weeks/months) vs waiting until the last minute.

Solution 2:

to schedule means to enter in a schedule or list (OED). This corresponds to the noun schedule, meaning any tabular or classified statement¹.

These can range from Train Schedules to Tax Schedules². They do not have to deal with future events. For example, the Prime Minister’s schedule of taxable sources of income and gains goes 'back 6 years'.

Another specific usage of the verb is given in the OED as a "draft addition" (January 2010) meaning To assign (a drug) to one of five classifications which place legal restrictions on availability and use.

An extended meaning of the verb is to place (something) on a programme of future events (OED).

So, the verb to schedule does not necessarily imply or even involve the future, any more than the noun means or implies the future.

If I want to schedule Friday's events, I can do that in advance or afterwards. For example, on Saturday I can sit down and schedule everything I did the day before. I can, if I want, do this on a schedule which can be 'a blank form to be filled up by the insertion of particulars under the several headings' (OED).

So, you can say schedule or, for clarity or emphasis, schedule in advance. Depending on context, schedule might be all you need to say, such as when you want to schedule a (future) dentist's appointment. Indeed your dentist may be able to schedule you on a walk-in basis or he may prefer to schedule you (or an appointment for you) in advance.

Since you haven't given any context for your question, that's as specific as I'd like to be.

¹classified here does not mean secret but arranged according to classification.

² "With reference to the British Income Tax, ‘Schedule A,’ ‘Schedule B,’ etc., are the official names for the forms of return applicable severally to the various classes into which sources of taxable income are divided" (OED). Tax Schedules are also used by the US Department of Internal Revenue.

OED = Oxford English Dictionary