How to get Current GMT date time in Magento 2?

You can get GMT Timezone in Magento by below code snippet,
Magento gives GMT timezone based on below function, Magento comes with DateTime php class, Magento\Framework\Stdlib\DateTime\DateTime is used for Forms GMT date.

Call from template file or php file by below way,

$dateModel = $this->dateTimeFactory->create();
echo $dateModel->gmtDate();

First Parameter is optional $format = null in gmtDate()
Default Format is Y-m-d H:i:s, You can add your time zone to convert normal timezone to GMT Timezone.

Result: 2018-09-09 11:22:49

Get orders collection between a date range in magento 2.

We just need to pass start date and end date to get collection between Specific time in Magento 2. We need to filter created_at field using addAttributeToFilter(). Create Block file.
By default created_at field in  sales_order table represent the time of order creation in Magento 2.

Call Function from template file,

You can get Order collection by date range by the above tricks.