diff --git a/doc/release-notes.md b/doc/release-notes.md
--- a/doc/release-notes.md
+++ b/doc/release-notes.md
@@ -3,3 +3,4 @@
   <https://download.bitcoinabc.org/0.16.3/>
 
 This release includes the following features and fixes:
+ - Add monolithactivationtime configuration in order to chose when the May, 15 hard fork activates. This value should not be changed in production, but it allows user to test the fork activation ahead of time.
diff --git a/src/validation.cpp b/src/validation.cpp
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -601,7 +601,9 @@
 
 static bool IsMonolithEnabled(const Config &config, int64_t nMedianTimePast) {
     return nMedianTimePast >=
-           config.GetChainParams().GetConsensus().monolithActivationTime;
+           gArgs.GetArg(
+               "-monolithactivationtime",
+               config.GetChainParams().GetConsensus().monolithActivationTime);
 }
 
 bool IsMonolithEnabled(const Config &config, const CBlockIndex *pindexPrev) {
diff --git a/test/functional/abc-p2p-compactblocks.py b/test/functional/abc-p2p-compactblocks.py
--- a/test/functional/abc-p2p-compactblocks.py
+++ b/test/functional/abc-p2p-compactblocks.py
@@ -83,6 +83,7 @@
                             '-limitdescendantcount=999999',
                             '-limitdescendantsize=999999',
                             '-maxmempool=99999',
+                            "-monolithactivationtime=%d" % MONOLITH_START_TIME,
                             "-excessiveblocksize=%d"
                             % self.excessive_block_size]]
 
diff --git a/test/functional/abc-p2p-fullblocktest.py b/test/functional/abc-p2p-fullblocktest.py
--- a/test/functional/abc-p2p-fullblocktest.py
+++ b/test/functional/abc-p2p-fullblocktest.py
@@ -47,6 +47,7 @@
         self.blocks = {}
         self.excessive_block_size = 100 * ONE_MEGABYTE
         self.extra_args = [['-whitelist=127.0.0.1',
+                            "-monolithactivationtime=%d" % MONOLITH_START_TIME,
                             "-excessiveblocksize=%d"
                             % self.excessive_block_size]]
 
@@ -180,7 +181,8 @@
         return block
 
     def get_tests(self):
-        self.genesis_hash = int(self.nodes[0].getbestblockhash(), 16)
+        node = self.nodes[0]
+        self.genesis_hash = int(node.getbestblockhash(), 16)
         self.block_heights[self.genesis_hash] = 0
         spendable_outputs = []
 
@@ -250,29 +252,37 @@
             block(n, spend=out[i], block_size=n * ONE_MEGABYTE // 2)
             yield accepted()
 
-        # Fork block
+        # Start moving MTP forward
         bfork = block(5555, out[15], block_size=8 * ONE_MEGABYTE)
-        bfork.nTime = MONOLITH_START_TIME
+        bfork.nTime = MONOLITH_START_TIME - 1
         update_block(5555, [])
         yield accepted()
 
         # Get to one block of the May 15, 2018 HF activation
-        for i in range(4):
+        for i in range(5):
             block(5100 + i)
             test.blocks_and_transactions.append([self.tip, True])
         yield test
 
+        # Check that the MTP is just before the configured fork point.
+        assert_equal(node.getblockheader(node.getbestblockhash())['mediantime'],
+                     MONOLITH_START_TIME - 1)
+
         # Before we acivate the May 15, 2018 HF, 8MB is the limit.
         block(4444, spend=out[16], block_size=8 * ONE_MEGABYTE + 1)
         yield rejected(RejectResult(16, b'bad-blk-length'))
 
         # Rewind bad block.
-        tip(5103)
+        tip(5104)
 
         # Actiavte the May 15, 2018 HF
-        block(5104)
+        block(5556)
         yield accepted()
 
+        # Now MTP is exactly the fork time. Bigger blocks are now accepted.
+        assert_equal(node.getblockheader(node.getbestblockhash())['mediantime'],
+                     MONOLITH_START_TIME)
+
         # block of maximal size
         block(17, spend=out[16], block_size=self.excessive_block_size)
         yield accepted()