Add 868MHz envs, fix MAC id, offset timesync

src/main.cpp

@@ -21,6 +21,7 @@ static SenderStatus g_sender_statuses[NUM_SENDERS];
 static bool g_ap_mode = false;
 static WifiMqttConfig g_cfg;
 static uint32_t g_last_timesync_ms = 0;
+static constexpr uint32_t TIME_SYNC_OFFSET_MS = 15000;
 
 static void init_sender_statuses() {
   for (uint8_t i = 0; i < NUM_SENDERS; ++i) {
@@ -124,6 +125,9 @@ static void sender_cycle() {
 }
 
 static void receiver_loop() {
+  if (g_last_timesync_ms == 0) {
+    g_last_timesync_ms = millis() - (TIME_SYNC_INTERVAL_SEC * 1000UL - TIME_SYNC_OFFSET_MS);
+  }
   LoraPacket pkt = {};
   if (lora_receive(pkt, 0) && pkt.protocol_version == PROTOCOL_VERSION && pkt.payload_type == PayloadType::MeterData) {
     uint8_t decompressed[256];