adjust for serial wait time during nRF52 bootup

src/main.h

@@ -30,6 +30,8 @@ extern uint32_t timeLastPowered;
 extern uint32_t rebootAtMsec;
 extern uint32_t shutdownAtMsec;
 
+extern uint32_t serialSinceMsec;
+
 // If a thread does something that might need for it to be rescheduled ASAP it can set this flag
 // This will supress the current delay and instead try to run ASAP.
 extern bool runASAP;