Uploading to S3 from memory and benchmarking it

I am running some very basic time commands on an S3 read/write. The problem is, I dont want it to be affected by system IO, and want to bench it from memory. A friend has suggested to use /dev/null as pipe, but I have a folder of 1000 files which is about 1GB in size. My bash command looks like this right now :

time aws s3 cp folder s3://mybucket/folder

What do you suggest, that will time only the write from memory? Many thanks