How much does a block’s recorded time differ from the actual time that my node first sees it?

A block has a “time” and a “mediantime”. Is it correct that the “time” is supposed to generally reflect the real time the block was mined and broadcast to the network? If so, how reliable is it? Assuming my node is well connected to other nodes, and sees all blocks within a few seconds after they are mined, how much can I expect the block’s “time” to differ from the actual time that my node first sees the block?