There’s no proof that prayers have any effect whatsoever, other than perhaps giving the person who prays a false sense of having done something. All claims that prayers have been answered are either anecdotal, fraudulent, delusional or are the result of either pure coincidence or confirmation bias.
How many prayers do you need in a day?
You get up and eat breakfast...you pray for another day of life
You go out in field service...you pray to Jehovah to give you strength, guidance
You eat lunch... you pray for your provision of food
You go to the Sunday meeting...there is an opening prayer to Jehovah and the Governing Body
You end the Watchtower Study meeting...you sing song and say a prayer
You eat dinner...you pray to Jehovah for your food
You go to bed...you pray to Jehovah for living one more day of life