An implantable system for performing cardiac resynchronization therapy, comprising: a first leadless pacemaker configured to be implanted in or on a right atrial chamber and selectively pace the RA chamber; a second leadless pacemaker configured to be implanted in or on a right ventricular chamber and selectively pace the RV chamber; a third leadless pacemaker configured to be implanted in or on a left ventricular chamber and selectively pace the LV chamber; one of the LP1, the LP2, or the LP3 designated a master LP; the LP1 also configured to sense a signal and measure a P-wave duration based on the signal sensed by the LP1; the LP1, or another one of the LPs (102b, 102c) that is designated the master LP, configured to determine an atrio-ventricular delay based on the measured P-wave duration; the LP2, or another one of the LPs (102a, 102c) that is designated the master LP, configured to determine a first AR or PR interval indicative of a time between an atrial depolarization and a ventricular depolarization in the RV chamber; the LP3, or another one of the LPs (102a, 102b) that is designated the master LP, configured to determine a second AR or PR interval indicative of a time between an atrial depolarization and a ventricular depolarization in the LV chamber; at least one of the LPs (102a, 102b, 102c) configured to determine an RV-LV delay indicative of a time it takes for a ventricular depolarization in the RV chamber to propagate to the LV chamber in response to the LP2 pacing the RV chamber; at least one of the LPs (102a, 102b, 102c) configured to determine an LV-RV delay indicative of a time it takes for a ventricular depolarization in the LV chamber to propagate to the RV chamber in response to the LP3 pacing the LV chamber; and the one of the LPs (102a, 102b, 102c) that is designated the master LP configured to determine a delta indicative of a difference between the first AR or PR interval and the second AR or PR interval, determine a correction factor indicative of a difference between the LV-RV delay and the RV-LV delay, and determine a VV delay based on the determined delta and the determined correction factor; wherein the LP1, the LP2, and the LP3 are configured to collectively perform CRT using the determined AV delay and the determined VV delay. a first leadless pacemaker configured to be implanted in or on a right atrial chamber and selectively pace the RA chamber; a second leadless pacemaker configured to be implanted in or on a right ventricular chamber and selectively pace the RV chamber; a third leadless pacemaker configured to be implanted in or on a left ventricular chamber and selectively pace the LV chamber; one of the LP1, the LP2, or the LP3 designated a master LP; the LP1 also configured to sense a signal and measure a P-wave duration based on the signal sensed by the LP1; the LP1, or another one of the LPs (102b, 102c) that is designated the master LP, configured to determine an atrio-ventricular delay based on the measured P-wave duration; the LP2, or another one of the LPs (102a, 102c) that is designated the master LP, configured to determine a first AR or PR interval indicative of a time between an atrial depolarization and a ventricular depolarization in the RV chamber; the LP3, or another one of the LPs (102a, 102b) that is designated the master LP, configured to determine a second AR or PR interval indicative of a time between an atrial depolarization and a ventricular depolarization in the LV chamber; at least one of the LPs (102a, 102b, 102c) configured to determine an RV-LV delay indicative of a time it takes for a ventricular depolarization in the RV chamber to propagate to the LV chamber in response to the LP2 pacing the RV chamber; at least one of the LPs (102a, 102b, 102c) configured to determine an LV-RV delay indicative of a time it takes for a ventricular depolarization in the LV chamber to propagate to the RV chamber in response to the LP3 pacing the LV chamber; and the one of the LPs (102a, 102b, 102c) that is designated the master LP configured to determine a delta indicative of a difference between the first AR or PR interval and the second AR or PR interval, determine a correction factor indicative of a difference between the LV-RV delay and the RV-LV delay, and determine a VV delay based on the determined delta and the determined correction factor; wherein the LP1, the LP2, and the LP3 are configured to collectively perform CRT using the determined AV delay and the determined VV delay.