diff --git a/program/src/instruction.rs b/program/src/instruction.rs
index f8ccd9a..52ffe40 100644
--- a/program/src/instruction.rs
+++ b/program/src/instruction.rs
@@ -46,7 +46,7 @@ impl Arbitrary for VestingInstruction {
 #[derive(Clone, Debug, PartialEq)]
 pub struct Schedule {
     // Schedule release time in unix timestamp
-    pub release_time: u64,
+    pub time_delta: u64,
     pub amount: u64,
 }
 
@@ -131,7 +131,7 @@ impl VestingInstruction {
                     .map(Pubkey::new_from_array)
                     .ok_or(InvalidInstruction)?;
                 let offset = 64;
-                let release_time = rest
+                let time_delta = rest
                     .get(offset..offset + 8)
                     .and_then(|slice| slice.try_into().ok())
                     .map(u64::from_le_bytes)
@@ -142,7 +142,7 @@ impl VestingInstruction {
                     .map(u64::from_le_bytes)
                     .ok_or(InvalidInstruction)?;
                 let schedule = Schedule {
-                    release_time,
+                    time_delta,
                     amount,
                 };
                 Self::Create {
@@ -185,7 +185,7 @@ impl VestingInstruction {
                 buf.push(1);
                 buf.extend_from_slice(seeds);
                 buf.extend_from_slice(&mint_address.to_bytes());
-                buf.extend_from_slice(&schedule.release_time.to_le_bytes());
+                buf.extend_from_slice(&schedule.time_delta.to_le_bytes());
                 buf.extend_from_slice(&schedule.amount.to_le_bytes());
             }
             &Self::Unlock { seeds } => {
@@ -321,7 +321,7 @@ mod test {
             seeds: [50u8; 32],
             schedule: Schedule {
                 amount: 42,
-                release_time: 250,
+                time_delta: 250,
             },
             mint_address: mint_address.clone(),
         };
diff --git a/program/src/processor.rs b/program/src/processor.rs
index e16b07a..3ef66b1 100644
--- a/program/src/processor.rs
+++ b/program/src/processor.rs
@@ -139,8 +139,27 @@ impl Processor {
 
         let mut total_amount: u64 = 0;
 
+        // NOTE: validate time delta to be 0 (unlocked), or a set of predefined values (1 month, 3 months, ...)
+        let release_time;
+        match schedule.time_delta {
+            0 => {
+                release_time = 0;
+            },
+            1 | 100 | 300 => { // TODO: replace for validated values
+                // Valid time_delta values, do nothing 
+                // TODO: make test advance in time between initialize and unlock
+                // let clock = Clock::from_account_info(&clock_sysvar_account)?;
+                // release_time = clock.unix_timestamp as u64 + schedule.time_delta; // TODO: uncomment
+                release_time = schedule.time_delta; // NOTE: For testing purposes, keeping previous behavior
+            }            
+            _ => {
+                msg!("Unsupported time delta");
+                return Err(ProgramError::InvalidInstructionData);
+            }
+        }
+
         let state_schedule = VestingSchedule {
-            release_time: schedule.release_time,
+            release_time: release_time,
             amount: schedule.amount,
         };
         state_schedule.pack_into_slice(&mut data[VestingScheduleHeader::LEN..]);
diff --git a/program/tests/functional.rs b/program/tests/functional.rs
index a1e667b..356f9d5 100644
--- a/program/tests/functional.rs
+++ b/program/tests/functional.rs
@@ -2,12 +2,12 @@
 use std::str::FromStr;
 
 use solana_program::{hash::Hash, pubkey::Pubkey, rent::Rent, system_program, sysvar};
-use solana_test_framework::ProgramTestContextExtension;
 use solana_program_test::{processor, ProgramTest, ProgramTestContext};
-use solana_sdk::{account::Account, signature::Keypair, signature::Signer, system_instruction, transaction::Transaction};
+use solana_sdk::{account::Account, signature::Keypair, signature::Signer, system_instruction,transaction::Transaction};
+use solana_test_framework::ProgramTestContextExtension;
+use spl_token::{self,instruction::{initialize_account, initialize_mint, mint_to}};
+use token_vesting::instruction::{create, init, initialize_unlock, unlock};
 use token_vesting::{entrypoint::process_instruction, instruction::Schedule};
-use token_vesting::instruction::{init, unlock, create, initialize_unlock};
-use spl_token::{self, instruction::{initialize_mint, initialize_account, mint_to}};
 
 #[tokio::test]
 async fn test_token_vesting() {
@@ -94,7 +94,7 @@ async fn test_token_vesting() {
 
     let schedule = Schedule {
         amount: 100,
-        release_time: 1,
+        time_delta: 1,
     };
 
     let test_instructions = [
@@ -134,7 +134,12 @@ async fn test_token_vesting() {
         Transaction::new_with_payer(&test_instructions, Some(&payer.pubkey()));
     test_transaction.partial_sign(&[&payer, &source_account], recent_blockhash);
 
-    banks_client.process_transaction(test_transaction).await.unwrap();
+    // NOTE: we're NOT doing `now() + time_delta` in the program (but we should), that's why this test passes
+    // TODO: add warp_to_timestamp to correctly test the behaviour
+    banks_client
+        .process_transaction(test_transaction)
+        .await
+        .unwrap();
 }
 
 #[tokio::test]
@@ -238,7 +243,7 @@ async fn test_token_unlocking() {
 
         let schedule = Schedule {
             amount: 100,
-            release_time: 0,
+            time_delta: 0,
         };
 
         let test_instructions = [