You need to be more specific (and musicians say "rhythm", not "timing"). Do you understand rhythmic notation properly? Are you playing wrong rhythms? Is your tempo fluctuating arbitrarily? Are you attempting rubato?

Like Scoth says we need more information. Are you missing rythms? is your beat or pulse not consistent?

If I were to take a stab at it I would guess many people refer to "timing" being off as a combination of not holding notes proper values and the beat pulse changing tempo (slow/fast/slow/fast).

If you are tapping your foot . . . STOP!!!
Don't beat your foot. I step on my students feet to keep them from tapping and they magically play in perfect tempo.

If you are holding notes wrong lengths make sure to sub-divide. Quarer notes are not quarter notes, they are 2 eighth notes together. Half-notes are 4 eighth notes. You need to hear or feel these eighth notes.

I know how you feel! I'm left handed to and i learnt the "normal" way. its good because you will be able to learnd more complicated fingering so much easier. as john said divide up your bars so that it is really easy to count. so maybe in 4/4 time a quaver could become "1" and a crotchet "1-2" so that you don't get confused by "1 & 2 &" etc. you will figure it out, i used to just guess at the start. it stops becoming easy to after a while! you will get better at it. count out loud if you have to. clap it out.

you may want to use a metronome. Tapping your foot for beats helps too.

@haruhiko i love your avatar. I love la corda d'oro it inspires me to practice more

Do not beat your foot.

Reason 1 - it is not reliable.
Reason 2 - it is a bad habit.
Reason 3 - If you get used to it you will do it in a concert and it looks realy really bad. (especially if you are not with the conductor)/.

when i was younger and about to learn a new piece. my teacher used to have me count out the "one, two, three, four" and while counting, i would then clap the note value. (or count "one and, two and, three and, four and" if that made it easier for me to get the note value)

i found just going over the rhythm first before attempting to play made a difference when it came to playing it on my violin.

sometimes, if i have difficulty with a new piece, I'll still do this. I find that at times it's easier to focus on one thing at time.

just the rhythm apposed to trying to hit the right note, proper bowing, being in tune and everything else there is to remember while playing.

get a metronome