I have decided not to worry about how much time I spend studying English.
I've decided not to worry about the time and just study as much English as I want to.
この場合、次のような言い方ができますよ。
ーI have decided not to worry about how much time I spend studying English.
「英語を勉強するのにどれだけ時間を費やすか気にしないことにした」
この言い方で、自分が好きなだけ英語を勉強することが言えます。
ーI've decided not to worry about the time and just study as much English as I want to.
「時間を気にせず、好きなだけ英語を勉強することにした」
to study as much English as I want to で「好きなだけ英語を勉強する」
ご参考まで！
I decided to study English as much as I like without worrying about the time.
I decided to devote as much time as I want to studying English without thinking about the time.
ご質問ありがとうございます。
① "I decided to study English as much as I like"＝「英語を好きなだけ勉強することに決めました」
"without worrying about the time."＝「時間を気にせずに。」
② "I decided to devote as much time as I want to studying English"＝「英語の勉強に好きなだけ専念することにしました」
"without thinking about the time."＝「時間のことを考えずに。」
ご参考までに。
カナダ 
アメリカ合衆国 
