Learn English – Use amount and quantity to replace number

"Time" can mean either the passage of time e.g. "time waits for no man", or an occasion or moment e.g. "we had a great time last night" . The passage of time is not countable, but occasions or moments are countable.

Other languages have different words for these which may be less confusing, e.g. in Portuguese, tempo often refers to time as in the passage of time, and altura means time as in an occasion or moment.

The image posted by the OP just tells me: wet sand, and Google images confirm the description.

A little investigation in Google books produced this:

She picked up a large handful of the wet sand and threw it at him. The children delighted in this and amid peals of laughter, ... Her hair was dripping wet and matted with sand.

_{The Witch's Daughter: Book Two}

I would strongly suggest that the OP write something like this:

‘… after rolling in the wet sand, my hair was matted.’

instead of this:

‘My hair was muddy after rolling in the mud’

The second version is grammatical and makes sense but the reader would have a very different image or idea from the first.

matted especially of hair or fur) tangled into a thick mass. (OD)

EDIT (because comments are ephemeral)

To me that image is wet sand, not mud, mud is sticky, thick goo. Wet sand when it is dried just becomes sand again. Generally speaking, a sandy beach consists of sand, a pebble beach consists of pebbles, a rocky beach ... etc. We use the expression sandcastle, not mud castle, when we talk about children filling buckets with wet sand and then turning them upside down. After a few hours in the sun, the castle dries and returns to being sand again.