How long this spell works?

Tom's Pov:

I once again looked around the garden, and I observed the flowers from the far end of the garden are started perishing. I am shocked and looked at them keenly, and they are perishing row by row towards us...

"They are coming..."

She immediately screamed out loudly with her nervous tone...

"Who?

Who is coming?"

I asked her with a confused tone...

"The descendants of the dark magic, my Lord...", she said with her worried scared tone, and I did not understand why she is worrying, "So what..?", I asked her by holding her chin and made her to look at me.

"They will kill us, my lord...", she said with her cry tone and immediately hugged me.

"I am there to protect you...", I said my patting on her back she nodded her head as ok and still hugged me tightly. I once again looked around, and by looking at the flowers perishing towards us, I can sense they are coming close to us.