The new building that Dick bought is nowhere near "done" or "liveable" yet, but Tim still has access and can (carefully) explore the building if he wants, which is what he's doing now. He knows TJ's working on the security system, but right now Tim's exploring and looking for opportune places for hidden passages, nooks, and hiding spots. It would be difficult to put any in that the other bats don't know about at this stage, but shut up, he's visualizing. Manifesting. Being reasonably careful not to fall through any questionable structures.