diff --git a/worker.go b/worker.go
index 379a875..887bb98 100644
--- a/worker.go
+++ b/worker.go
@@ -76,7 +76,7 @@ func (w *goWorker) finish() {
 	w.task <- nil
 }
 
-func (w *goWorker) when() time.Time {
+func (w *goWorker) lastUsedTime() time.Time {
 	return w.lastUsed
 }
 
diff --git a/worker_func.go b/worker_func.go
index 0743506..701a076 100644
--- a/worker_func.go
+++ b/worker_func.go
@@ -76,7 +76,7 @@ func (w *goWorkerWithFunc) finish() {
 	w.args <- nil
 }
 
-func (w *goWorkerWithFunc) when() time.Time {
+func (w *goWorkerWithFunc) lastUsedTime() time.Time {
 	return w.lastUsed
 }
 
diff --git a/worker_loop_queue.go b/worker_loop_queue.go
index 89e8112..e8f481f 100644
--- a/worker_loop_queue.go
+++ b/worker_loop_queue.go
@@ -115,7 +115,7 @@ func (wq *loopQueue) binarySearch(expiryTime time.Time) int {
 	nlen = len(wq.items)
 
 	// if no need to remove work, return -1
-	if wq.isEmpty() || expiryTime.Before(wq.items[wq.head].when()) {
+	if wq.isEmpty() || expiryTime.Before(wq.items[wq.head].lastUsedTime()) {
 		return -1
 	}
 
@@ -137,7 +137,7 @@ func (wq *loopQueue) binarySearch(expiryTime time.Time) int {
 		mid = l + ((r - l) >> 1)
 		// calculate true mid position from mapped mid position
 		tmid = (mid + basel + nlen) % nlen
-		if expiryTime.Before(wq.items[tmid].when()) {
+		if expiryTime.Before(wq.items[tmid].lastUsedTime()) {
 			r = mid - 1
 		} else {
 			l = mid + 1
diff --git a/worker_loop_queue_test.go b/worker_loop_queue_test.go
index 5dac504..c5ad8a9 100644
--- a/worker_loop_queue_test.go
+++ b/worker_loop_queue_test.go
@@ -118,7 +118,7 @@ func TestRotatedArraySearch(t *testing.T) {
 	// [expiry4, time, time, time,  time, expiry5,  time, time, time, time/head/tail]
 	assert.EqualValues(t, -1, q.binarySearch(expiry2), "index should be -1")
 
-	assert.EqualValues(t, 9, q.binarySearch(q.items[9].when()), "index should be 9")
+	assert.EqualValues(t, 9, q.binarySearch(q.items[9].lastUsedTime()), "index should be 9")
 	assert.EqualValues(t, 8, q.binarySearch(time.Now()), "index should be 8")
 }
 
diff --git a/worker_queue.go b/worker_queue.go
index b0da75d..3792a55 100644
--- a/worker_queue.go
+++ b/worker_queue.go
@@ -16,7 +16,7 @@ var (
 type worker interface {
 	run()
 	finish()
-	when() time.Time
+	lastUsedTime() time.Time
 	inputFunc(func())
 	inputParam(interface{})
 }
diff --git a/worker_stack.go b/worker_stack.go
index f8c7fa9..418dbf1 100644
--- a/worker_stack.go
+++ b/worker_stack.go
@@ -64,7 +64,7 @@ func (wq *workerStack) binarySearch(l, r int, expiryTime time.Time) int {
 	var mid int
 	for l <= r {
 		mid = (l + r) / 2
-		if expiryTime.Before(wq.items[mid].when()) {
+		if expiryTime.Before(wq.items[mid].lastUsedTime()) {
 			r = mid - 1
 		} else {
 			l = mid + 1