The concept of a standard translation page is important as this is a sure way to set a standard in work and pricing. For instance, a page with a lot of text and little space between the lines certainly can’t be considered equal to a page full of photos and with just a few lines. This wouldn’t be fair, not to the clients in terms of pricing, not to the translator in terms of the time and effort invested.
An experienced translator needs about an hour on average to translate a single translation page, but this depends on the complexity of the text, amount of specialist terms, available resources, but also the language that the translator is translating to. Basically, translating to the native language is always easier (and preferable). So, sometimes it takes half an hour to translate a standard translation page, but it may also take a few hours.
In some cases, e.g. when the word count is available, but the character count is not, as is the case with ppt or pptx, i.e. PowerPoint files, one standard translation page is equal to 250 words.