I look for a shloka that I can chant throughout the day, for worship of Surya Deva (Aditya Hridayam is too long). Can someone recommend any?
There are many shlokas and stotras to worship Surya. Some recommend Gayatri Mantra because it's dedicated to Savitr i.e., Surya but there are specific way to chant the mantra like pronunciation, performing mudras for unlocking, dhyana to Gayatri etc., Hence that should not be chanted throughout the day.
Some stotras are Surya Ashtakam containing 8 shlokas. It doesn't take more than 5 minutes if you are good at reading Sanskrit.
There is a shloka which is a part of Navagraha Stotra.
Japākusuma saṃkāśaṃ kāśyapeyaṃ mahādyutiṃ
tamoriṃ sarvapāpaghna praṇatosmi divākaram
Meaning : I pray to the Sun, who shines in the colour of Hibiscus, descendant of Kashyapa, extremely brilliant, who is enemy of darkness (creator of light), destroyer of all the sins.
There are quite a few mantras regarding the Sun , most famous is Gayathri Manthra. But i think , Moola Manthra fits the bill here , its short and very powerful,this is even sometimes called Bija manthra.
The Verse is "Om Hrim Sum Suryaya Namah" , please find the references for the same, Surya Bija Manthra The Bija manthras need to be pronounced , as the vibrations has various benefits.
One of the main benefits include improved eyesight and concentration.
There are many bija manthras in existence including vasudeva , Lakshmi , Guru and many more .
Hope this helps.