Tax depends on which category your items falls into. Sometime customs put wrong category on item if they are not familiar with the item. If you disagree with classification, then you may need to provide proof that the category they put it in is wrong. Proof can be in form of leaflet of product description and purpose.

As soon as they satisfied with explanation, then you just need to pay the amount of tax and your item can be released as soon as the officer got the document stamped. Agent will take longer time sometimes because they are also doing clearance for many customers but probably within few days if the item has no problem with customs. You probably can clear it within the same day or even hours.

If you are lazy to do by yourself, just appoint POS to do the clearance. Maybe just few days. You can call POS to ask how soon you can get your item. I have no idea how much they charge though. Very long long long time ago I did my clearance but it was for a bulk of personal items I shipped back to Malaysia. Have no experience at all and ask the officer how. He guided me and give sample on how to fill form. I got everything cleared in about 40 min. The officer told me to look at all those agents. Those agents (perhaps newbies) probably spent the whole day. He was there for those who needed help but no one was asking and said. "You get yours done in less than an hour." I just smiled and thanked him

Freight Forwarder or agents don't really bother if the declaration of category is correct or not. They are not technical people. Sometimes, they get back to you to ask and sometimes don't. They just tell you how much tax you need to pay.