Added the ability to parametrize Teensy 3 core USB init delays through compiler defines (TEENSY_INIT_USB_DELAY_BEFORE, TEENSY_INIT_USB_DELAY_AFTER). When defines are not present, default values are used, depending on teensy version.

teensy3/pins_teensy.c

 	TPM1_SC = FTM_SC_CLKS(1) | FTM_SC_PS(0);
 #endif
 	analog_init();
+
+#if !defined(TEENSY_INIT_USB_DELAY_BEFORE)
+	#if TEENSYDUINO >= 142
+		#define TEENSY_INIT_USB_DELAY_BEFORE 25
+	#else
+		#define TEENSY_INIT_USB_DELAY_BEFORE 50
+	#endif
+#endif
+
+#if !defined(TEENSY_INIT_USB_DELAY_AFTER)
+	#if TEENSYDUINO >= 142
+		#define TEENSY_INIT_USB_DELAY_AFTER 275
+	#else
+		#define TEENSY_INIT_USB_DELAY_AFTER 350
+	#endif
+#endif
+
 	// for background about this startup delay, please see these conversations
 	// https://forum.pjrc.com/threads/36606-startup-time-(400ms)?p=113980&viewfull=1#post113980
 	// https://forum.pjrc.com/threads/31290-Teensey-3-2-Teensey-Loader-1-24-Issues?p=87273&viewfull=1#post87273
-#if TEENSYDUINO >= 142
-	delay(25);
-	usb_init();
-	delay(275);
-#else
-	delay(50);
+
+	delay(TEENSY_INIT_USB_DELAY_BEFORE);
 	usb_init();
-	delay(350);
-#endif
+	delay(TEENSY_INIT_USB_DELAY_AFTER);
 }