Generally the advice is don't tell your manager that you have a job interview. That makes them not trust you and nervous that you will quit any day now.
That advice might be different if you are on a contract with a deadline. The temp-to-hire is like that. Your manager knows your goal is full-time employment. They either will make you an offer if they like your work, and they have the budget, or they will risk you leaving. Letting them know you are getting nervous about the end of the temp period can be beneficial to getting them to make a decision.
You are on a probationary contract with no benefits. Therefore no specific vacation and holiday pay. You have to review your contract to see if you have to charge 40 hours every week to use all the money before the contract runs out. Your contract or some sort of handbook should specify how to inform them you will be out of the office for a short appointment.
Normally people hide interviews by calling them doctors appointments. This works great when they have one bucket of PTO instead of separate vacation and sick leave accounts. Many people make the interviews for the start or end of thee day to mask what is going on.
Unless the time remaining on the contract is very short I wouldn't schedule more than one or two in a week, otherwise it can impact your performance.
If you are going to tell them, be polite, tell them you want to give them a heads up that you are interviewing. Remember the goal is to get them to hire you, not to get them to fire you.