Yes! In California, bonds can be posted twenty-four hours a day, seven days per week. But whether you can bail someone out of jail at any time depends on their situation.
Unlike bonds in state courts, federal bonds are not automatically set. Instead, the defendant appears before a federal magistrate judge for a specific bail determination. States use a bail schedule. Federal courts do not use a bail schedule.
You need to file a motion to amend bond conditions with the court. You should at least consult with a local criminal defense attorney (if you are not already represented by someone) to discuss the issues the court will consider, and the best way to address those issues.
The defendant can post their own bail or ask a family member or friend to post it. If the defendant uses a bond company, the company may require the defendant to have a co-signer (someone who will help the company find the defendant should they fail to appear).
And while some will tell you that you can't remain anonymous, the short answer is actually yes, you can. (But with one major consideration.) The Court is going to need a name and person to return the bond to once the court date has been successfully completed.
The bail bond agent will need you to sign some paperwork in order for you to secure their services. This usually means paying an amount to the agent, usually a percentage of the total bail amount, and signing off on any collateral for the bond.