Ship times for all iPad 2 models now sit at 3 to 4 weeks. Early birds who woke up yesterday could get their orders shipped in 3 to 5 days.

While some iPad 2 buyers have been surprised to see their online orders ship early, new buyers are seeing wait times for new orders extended yet again.

Apple today quietly pushed the ship times for iPad 2 online orders back once again, now estimating new purchases at 3 weeks to a month.

The new shipping times, along with sellouts, and limited model availability at retail stores (including its own), are a clear sign that Apple is having a tough time meeting demand. A similar situation took place during the first launch, leading to Apple pushing back its international launch, which for the iPad 2 is less than two weeks away.

Online sales of the iPad 2 kicked off at 1 a.m. PT yesterday, and quickly went from 3 to 5 days to 2 to 3 weeks, the latter of which had held until just a few hours ago.

Unlike last year's sales, Apple is not allowing users to reserve iPads from its retail stores. This process would allow users to pick an iPad model they wanted, and get an e-mail when it was available for pickup and purchase.

Analysts like Piper Jaffray's Gene Munster set estimates for first day sales somewhere between 400,000 to 500,000 units, some 200,000 better than the first iPad did during the same time period in its launch. Brian Marshall, an analyst at Gleacher & Co. set the bar a bit higher, at 600,000. Apple is expected to unveil preliminary unit sales on Monday, as it did on the Monday following the launch of the first iPad.