It depends on the country you will be based in. Different country, different contract, with different part time options and rules.
Some options are available on a seniority basis and require a long time in the company, depending on the rank as well, other options are easier to get.
The first year would normally be full time, unless hired on a seasonal base.
I am assuming you have been hired already or have a start date? Because I would not make life changing career decisions based on the part time options of a single operator you are not even working for, especially one like easyjet, very picky when it comes to direct entry FOs and CPTs, especially in recent times.