php date_diff not working

Keyword Analysis

Keyword	CPC	PCC	Volume	Score	Length of keyword
php date_diff not working	0.47	0.3	8439	4	25
php	1.24	0.5	1763	74	3
date_diff	1.02	0.5	4047	26	9
not	1.29	0.1	4978	65	3
working	1.32	0.4	9375	64	7

Keyword	CPC	PCC	Volume	Score
php date_diff	1.74	0.8	1435	50
php date_diff in days	0.58	0.9	4461	74
php day_diff	1.44	1	6659	86
date diff php days	1.73	0.4	6658	34
time diff in php	0.47	0.6	4796	19
php date diff in minutes	0.83	0.4	7443	87
date_diff	1.59	0.6	8850	7
php datetime diff invert	1.58	0.8	9491	83
how to get date difference in php	0.16	0.9	8325	10
datetime_diff	1.76	0.1	1678	59
diff_date	0.46	0.9	9324	8
php date difference in days	0.78	0.6	9608	89
python date_diff	0.05	0.6	6726	29
new date php difference	0.07	1	6244	29
php datetime difference in days	0.48	0.8	8965	49
mysql diff_date	1.47	0.1	5164	42
php date difference	0.81	0.4	5860	93
php date_diff format	0.21	0.7	5852	16
php date_diff function	0.77	0.7	9918	53
php date_diff months	1.75	0.7	930	8
php date_diff weeks	1.45	0.6	8644	50
php date_diff minutes	1.19	0.8	50	77
date diff in php	0.19	1	1308	72
php calculate date difference in days	0.6	0.2	485	16
php get date difference in days	1.12	1	122	76