Evidence time is sourced from block time (#138)

spec/abci/abci.md

@@ -574,9 +574,8 @@ via light client.
   - `Type (string)`: Type of the evidence. A hierarchical path like
     "duplicate/vote".
   - `Validator (Validator`: The offending validator
-  - `Height (int64)`: Height when the offense was committed
-  - `Time (google.protobuf.Timestamp)`: Time of the block at height `Height`.
-    It is the proposer's local time when block was created.
+  - `Height (int64)`: Height when the offense occured
+  - `Time (google.protobuf.Timestamp)`: Time of the block that was committed at the height that the offense occured
   - `TotalVotingPower (int64)`: Total voting power of the validator set at
     height `Height`
 

spec/core/data_structures.md

@@ -221,7 +221,8 @@ type Evidence interface {
 
 All evidence can be encoded and decoded to and from Protobuf with the `EvidenceToProto()` 
 and `EvidenceFromProto()` functions. The [Fork Accountability](../consensus/light-client/accountability.md) 
-document provides a good overview for the types of evidence and how they occur.
+document provides a good overview for the types of evidence and how they occur. Each evidence uses
+the timestamp of the block that the evidence occured at to indicate the age of the evidence. 
 
 `DuplicateVoteEvidence` represents a validator that has voted for two different blocks 
 in the same round of the same height. Votes are lexicographically sorted on `BlockID`.
@@ -230,6 +231,8 @@ in the same round of the same height. Votes are lexicographically sorted on `Blo
 type DuplicateVoteEvidence struct {
 	VoteA  *Vote
 	VoteB  *Vote
+
+	Timestamp time.Time
 }
 ```
 
@@ -253,6 +256,8 @@ type LunaticValidatorEvidence struct {
 	Header             *Header 
 	Vote               *Vote  
 	InvalidHeaderField string
+
+	Timestamp time.Time
 }
 ```