Fixup multi-collator parachain transition to async backing (paritytec…

…h#3510)

Fixing: 
```
Verification failed for block 0x07bbf1e04121d70a4bdb21cc055132b53ac2390fa95c4d05497fc91b1e8bf7f5 received from (12D3KooWJzLd8skcAgA24EcJey7aJAhYctfUxWGjSP5Usk9wbpPZ): "Header 0x07bbf1e04121d70a4bdb21cc055132b53ac2390fa95c4d05497fc91b1e8bf7f5 rejected: too far in the future"   
```

---------

Signed-off-by: Alexandru Gheorghe <alexandru.gheorghe@parity.io>
Co-authored-by: Dmitry Sinyavin <dmitry.sinyavin@parity.io>
Co-authored-by: s0me0ne-unkn0wn <48632512+s0me0ne-unkn0wn@users.noreply.github.com>
Co-authored-by: Bastian Köcher <git@kchr.de>

substrate/bin/node-template/node/src/service.rs

@@ -80,23 +80,29 @@ pub fn new_partial(config: &Configuration) -> Result<Service, ServiceError> {
 		telemetry.as_ref().map(|x| x.handle()),
 	)?;
 
-	let slot_duration = sc_consensus_aura::slot_duration(&*client)?;
-
+	let cidp_client = client.clone();
 	let import_queue =
 		sc_consensus_aura::import_queue::<AuraPair, _, _, _, _, _>(ImportQueueParams {
 			block_import: grandpa_block_import.clone(),
 			justification_import: Some(Box::new(grandpa_block_import.clone())),
 			client: client.clone(),
-			create_inherent_data_providers: move |_, ()| async move {
-				let timestamp = sp_timestamp::InherentDataProvider::from_system_time();
+			create_inherent_data_providers: move |parent_hash, _| {
+				let cidp_client = cidp_client.clone();
+				async move {
+					let slot_duration = sc_consensus_aura::standalone::slot_duration_at(
+						&*cidp_client,
+						parent_hash,
+					)?;
+					let timestamp = sp_timestamp::InherentDataProvider::from_system_time();
 
-				let slot =
-					sp_consensus_aura::inherents::InherentDataProvider::from_timestamp_and_slot_duration(
-						*timestamp,
-						slot_duration,
-					);
+					let slot =
+						sp_consensus_aura::inherents::InherentDataProvider::from_timestamp_and_slot_duration(
+							*timestamp,
+							slot_duration,
+						);
 
-				Ok((slot, timestamp))
+					Ok((slot, timestamp))
+				}
 			},
 			spawner: &task_manager.spawn_essential_handle(),
 			registry: config.prometheus_registry(),