Dear Rabbi Simon,
I just now remembered to count the Omer from last night! In looking at my watch, I see that it is now 20:07, and sunset (according to my app) is 20:05. However I think that I actually began the counting (with the short declaration of intent, “behold I am prepared and ready…”) at 20:04, ie just before sunset. Am I considered to have missed the day of counting, or have I fulfilled the mitzvah (albeit quite belatedly) and therefore I can continue counting night by night with a blessing every time until Shavuot. (For the purposes of this Q I am generously assuming that I will remember every night from now on.)
TY for your reply, as I need to know if I can count 10 days of the ‘Omer after dark tonight!
TY for your timely Q. The answer is that you may/should continue to count with a berachah. The posekim say that this is a case of a s’fek s’feika (a “double doubt”): Perhaps the halakhah is in accordance with the (majority) opinion that one may/should recite a beracha every night, even if s/he has forgotten one or more day along the way. And in addition, a few minutes after sunset (at least 9, and probably up to 20 minutes or more) may still be regarded as belonging to the previous day (in which case you have indeed performed the mitzvah for yesterday, even if you narrowly missed the moment of sunset itself).
I hope this is helpful, and may even be the answer you were counting on.