The Arbitrum Foundation Administrative Budget Wallet implements the contract specified in AIP-1.1. The wallet escrows funds which are unlocked over a linear four year schedule; once unlocked, funds can be claimed by a multisig wallet controlled by the Arbitrum Foundation.
Escrowed $ARB cannot be used to vote on governance proposals. Additionally, the Budget Wallet delegates its votes to the "exclude address" (see "Vote Exclusion"); thus, its escrowed $ARB isn't counted towards the governance quorum denominator.
As per AIP-1.1, the DAO has the ability to change the Budget Wallet's unlock schedule. This can be done via a governance proposal which migrates the wallet's funds to a new wallet which enforces a new schedule (see here for test code). Note that the DAO is also the proxy-owner of the Budget Wallet and thus could vote to upgrade its implementation logic arbitrarily; however, for adjusting its unlock schedule, the migration method is the preferable recommendation.