Update preview explorer url and logic

sync_tests/utils/explorer.py

@@ -12,7 +12,7 @@
 TESTNET_EXPLORER_URL = "https://explorer.cardano-testnet.iohkdev.io/graphql"
 SHELLEY_QA_EXPLORER_URL = "https://explorer.shelley-qa.dev.cardano.org/graphql"
 PREPROD_EXPLORER_URL = None
-PREVIEW_EXPLORER_URL = None
+PREVIEW_EXPLORER_URL = "https://preview.koios.rest/api/v1/epoch_info?_epoch_no="
 
 EXPLORER_URLS = {
     "mainnet": MAINNET_EXPLORER_URL,
@@ -60,6 +60,9 @@ def get_epoch_start_datetime_from_explorer(env: str, epoch_no: int) -> str | Non
         )
         return None
 
+    if env == "preview":
+        url = f"{url}{epoch_no}"
+
     result = None
     try:
         response = requests.post(url, data=payload, headers=headers)
@@ -71,6 +74,8 @@ def get_epoch_start_datetime_from_explorer(env: str, epoch_no: int) -> str | Non
                 "!!! ERROR: status_code != 200 when getting start time for "
                 f"epoch {epoch_no} on {env}"
             )
+        elif env == "preview":
+            result = response.json()[0]["start_time"]
         else:
             count = 0
             while "data" in response.json() and response.json().get("data") is None: