add note about delaying use of builder network through Merge

specs/validator.md

@@ -46,6 +46,7 @@ and by extension the [Bellatrix consensus specs][bellatrix-specs].
 | - | - | - |
 | `EPOCHS_PER_VALIDATOR_REGISTRATION_SUBMISSION` | 1 | epoch(s)|
 | `BUILDER_PROPOSAL_DELAY_TOLERANCE` | 1 | second(s) |
+| `MERGE_DELAY` | 16 | epoch(s) |
 
 ## Validator registration
 
@@ -149,10 +150,14 @@ network.
 
 ## Responsibilites during the Merge transition
 
-Honest validators will not utilize the external builder network until after the transition from the proof-of-work chain
-to the proof-of-stake beacon chain has been finalized by the proof-of-stake validators. This requirement is in place
-to reduce the overall technical complexity of the Merge. Concretely this means a honest validator client will not use
-any of the builder APIs or run any builder software until the Merge has finalized.
+Honest validators will not utilize the external builder network during the transition from proof-of-work to
+proof-of-stake. This requirement is in place to reduce the overall technical complexity of the Merge.
+
+Concretely, honest validators **MUST** wait until `MERGE_DELAY` epochs after the transition has been finalized before
+they can start querying the external builder network. See [EIP-3675](eip-3675) for further details about the transition
+process itself.
+
+* NOTE: if the merge transition happens in epoch N and is finalized in epoch N+2, then proposers **MUST** not use the external builder network until epoch N + 2 + `MERGE_DELAY`.
 
 [builder-spec]: ./builder.md
 [builder-spec-apis]: ./builder.md#endpoints
@@ -162,3 +167,4 @@ any of the builder APIs or run any builder software until the Merge has finalize
 [beacon-node-apis]: https://ethereum.github.io/beacon-APIs
 [bellatrix-specs]: https://github.com/ethereum/consensus-specs/blob/dev/specs/bellatrix
 [bellatrix-validator-specs]: https://github.com/ethereum/consensus-specs/blob/dev/specs/bellatrix/validator.md
+[eip-3675]: https://eips.ethereum.org/EIPS/eip-3675