In King County, when someone is arrested for a felony such as robbery, they will be held without bail until they see a judge. If your boyfriend was arrested yesterday, he will be seeing a judge this afternoon. The judge today will set bail. Your boyfriend will them see a judge again on Tuesday afternoon to be advised whether charges are filed against him or not. If charges are filed by then, he will be given an arraignment date. If charges are not filed by Tuesday afternoon, he will be released unconditionally, but the state still had three years to file charges.
Your first step should be to discuss this situation directly with an experienced criminal defense attorney to discuss the details of the allegation, and what steps can be taken right away to get him out of custody.